Research ArticleSpondyloarthritis

Complement Proteins L-Ficolin and M-Ficolin Are Increased in Patients With Axial Spondyloarthritis and Decrease After Tumor Necrosis Factor Inhibitor Treatment

Clara Elbæk Mistegaard, Anne Troldborg, Annette Hansen, Steffen Thiel, Anne Grethe Jurik, Rosa M. Kiil, Alice A. Christiansen, Berit Schiøttz-Christensen, Oliver Hendricks, Susanne Juhl Pedersen, Inge Juul Sørensen, Mikkel Østergaard and Anne Gitte Loft
The Journal of Rheumatology January 2024, 51 (1) 31-38; DOI: https://doi.org/10.3899/jrheum.2023-0164

Abstract

Objective We have previously reported elevated levels of the complement lectin pathway proteins L-ficolin and H-ficolin in patients with axial spondyloarthritis (axSpA) compared with healthy controls. The aim of the present study was to investigate these biomarkers in a cross-sectional cohort of patients suffering from low back pain (LBP). Further, we aimed to investigate changes in lectin pathway protein levels after initiation of adalimumab (ADA; a tumor necrosis factor inhibitor) in a longitudinal cohort of patients with axSpA.

Methods Lectin pathway protein levels (mannan-binding lectin [MBL], collectin liver 1, H-ficolin, L-ficolin, M-ficolin, MBL-associated serine protease [MASP]-1, MASP-2, MASP-3, MBL-associated protein 19 [MAp19], and MAp44) in EDTA plasma were determined in 2 well-characterized cohorts: (1) a clinical cross-sectional cohort of patients with LBP, including patients with axSpA (n = 23), patients with unspecific LBP (uLBP) with ≥ 1 SpA features (n = 55), and patients with uLBP without SpA features or magnetic resonance imaging findings suggestive of axSpA (n = 64); and (2) a randomized double-blinded, placebo-controlled trial cohort of patients with axSpA (n = 49) initiating ADA therapy. Lectin pathway protein levels were determined using immunoassays.

Results Plasma levels of L-ficolin and M-ficolin were significantly increased in the cross-sectional cohort of newly diagnosed patients with axSpA compared with clinically relevant controls with uLBP (all P < 0.05). Both L-ficolin and M-ficolin decreased significantly after ADA therapy (P < 0.05).

Conclusion L-ficolin and M-ficolin levels are elevated in newly diagnosed patients with axSpA compared with clinically relevant controls. Both L-ficolin and M-ficolin levels decrease significantly after initiating ADA therapy. These findings provide new insights into the inflammatory processes in axSpA and support the involvement of complement in axSpA pathogenesis.

Key Indexing Terms:

Axial spondyloarthritis (axSpA) is a common chronic rheumatic disease affecting approximately 0.5% to 1.5% of the population in Western Europe.1 The condition is characterized by inflammation of the axial skeleton, including the spine and the sacroiliac joints, potentially followed by progressive ankylosis of these joints.1 The disease often starts in the third decade of life and has significant personal and socioeconomic consequences.

Despite significant efforts, including the introduction of magnetic resonance imaging (MRI) of the sacroiliac joints and spine, the time from symptom onset to diagnosis remains 6 to 8 years.2,3 Several treatments have been shown to reduce pain and stiffness and improve quality of life, including regular physiotherapy, exercise, and nonsteroidal antiinflammatory drugs (NSAIDs),4 as well as tumor necrosis factor inhibitors (TNFi), interleukin (IL)-17A, and Janus kinase inhibitors (JAKi) if the first-line treatments are insufficient. Further, TNFi is considered to reduce further development of chronic structural damage after several years of treatment.5,6 This underlines the need for tools to improve early diagnosis. Thus, the search for an improved understanding of the unclear pathogenesis, as well as new diagnostic biomarkers of early axSpA, remains of significant clinical interest. We have previously reported elevated plasma levels of the complement lectin pathway proteins L-ficolin and H-ficolin in patients with axSpA compared with healthy blood donors.7 Current evidence suggests that the innate immune system is involved in the pathogenesis of axSpA.8,9 Animal models have also shown inhibition of complement to limit structural damage associated with the disease.10

The complement system is a cornerstone of the innate immune system. Activation of the complement system proceeds through 3 distinct pathways: the alternative pathway, the classical pathway, and the lectin pathway (LP). All 3 pathways converge in a shared terminal cell-lytic pathway or cause opsonization for elimination by phagocytosis.11 The result is the clearing of microorganisms, apoptotic cells, or cellular debris.12 The complement system is thus multifaceted, and essential in host defense, homeostasis, and the development of certain cell types (eg, B cells).13 More broadly in the organism, the lack of either mannan-binding lectin (MBL)-associated serine protease (MASP)-3 or collectin-LK (CL-LK) results in a developmental deficiency called 3MC syndrome (comprising Malpuech, Michels, Mingarelli, and Carnevale syndromes).12,14,15 The LP is specifically initiated when pattern-recognition molecules (PRMs), such as MBL, CL-LK, H-ficolin, L-ficolin, and M-ficolin (the latter 3 also known as ficolin-3, ficolin-2 and ficolin-1, respectively), bind to a fitting pattern that leads to downstream complement activation and the effector mechanisms stated above. The complement system plays a pivotal role in connecting innate immunity, the clearance of infections, the maintenance of homeostasis, and various aspects of human development. These elements are especially noteworthy in the context of axSpA, given the hypothesis that the microbiome may contribute to its pathogenesis.16

In this project, we aimed to further investigate a panel of LP proteins in a cohort of patients with newly diagnosed axSpA compared to other patients with low back pain (LBP). Further, we aimed to examine changes in LP protein plasma levels in a double-blinded randomized controlled trial (RCT) in which patients with axSpA initiated adalimumab (ADA) therapy or placebo for 12 weeks and thereafter ADA for 36 weeks.

METHODS

Study populations. The study population in the Molecular Biology of Infectious Agents in the Early Diagnosis of Spondyloarthritis (MICSA) cohort has been described in detail previously.17-19 Briefly, patients were recruited from the Southern Spine of Denmark (SSD) cohort,20 a clinical cohort of patients aged 18-40 with LBP referred to a spine center for evaluation including MRI. The MICSA study population included (1) 23 patients with axSpA based on retrospective multidisciplinary conference consensus (involving both rheumatologists and radiologists) after 3.5 years of follow-up; (2) 55 patients with unspecific LBP (uLBP) who were not considered to have axSpA based on the multidisciplinary team conference consensus but had ≥ 1 SpA features as defined by Assessment of SpondyloArthritis international Society (ASAS) 2009 criteria, defined in our study as “uLBP + SpA features”; and (3) 64 patients with uLBP and without SpA features or MRI findings suggestive of axSpA, termed “uLBP – SpA features.”

In the Danish Multicenter Study of Adalimumab in Spondyloarthritis (DANISH) cohort, 52 patients with axSpA according to the European Spondyloarthritis Study Group (ESSG), and with sacroiliitis shown by radiograph and/or MRI as well as Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) > 4 despite treatment with at least 2 NSAIDs, were randomized to receive subcutaneous injections of ADA 40 mg or placebo every other week.21 From week 12, all participants received the TNFi ADA until week 48. Clinical assessments and MRI scans were performed at weeks 0, 12, 24, and 48.

MICSA cohort methodology. The scan protocols have been published previously.22 Briefly, the MRI scans of the spine and sacroiliac joints were performed on a 1.5T MRI unit (Philips Achieva). Sacroiliac joint MRI included semicoronal T1-weighted and T1-weighted fat-saturated sequences, and semiaxial short tau inversion recovery (STIR) sequences. Spine MRI included sagittal T1-weighted and STIR sequences of the entire spine, as well as a 3-D T2-weighted sequence of the lumbar spine and axial T2-weighted images at the 3 lowest intervertebral spaces.

MRI scans were assessed according to ASAS 2009 criteria at inclusion in the SSD cohort20 and evaluated as a part of a clinical diagnostic approach at the retrospective multidisciplinary team conference, as described in detail previously.18 Patients with uLBP without suspicion of axSpA were only evaluated at baseline.17

EDTA plasma samples were collected from the study participants and centrifuged at 2000 g for 10 minutes. Each sample was frozen at −80°C after collection, then thawed and diluted one-quarter in Tris-buffered saline (TBS; 10 mM Tris, 145 mM NaCl, pH 7.4) prior to measurements of complement LP proteins. Samples from the 3 patient groups were analyzed for HLA-B27 and levels of high-sensitivity C-reactive protein (CRP; considered normal ≤ 6 mg/L).17

DANISH cohort methodology. The MRI protocol has been published previously.21 Briefly, MRI scans of sacroiliac joints and spine were performed at a 1.5T MRI unit. Sagittal spine images included STIR sequences and T1-weighted turbo spin echo sequences before and after intravenous injection of 0.1 mmol/kg body weight of the gadolinium-containing contrast agent Gadodiamide (Omniscan, GE Healthcare). Postcontrast images were obtained with fat saturation. Sacroiliac joint images included semicoronal and semiaxial STIR and semicoronal T1-weighted sequences.

MRI scans were anonymized and evaluated blind to chronology and clinical data. SJP evaluated the MRI scans according to the Spondyloarthritis Research Consortium of Canada (SPARCC) spine and sacroiliac joint inflammation scores23,24 as well as the SPARCC sacroiliac joint structural scores for fat, erosion, backfill, and ankylosis.25 The spine MRI scans were also evaluated according to the Canada-Denmark scoring system for bone marrow edema, fat, erosion, and new bone formation.26,27 Radiographs of the spine and sacroiliac joints were assessed according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) and modified New York (mNY) criteria, respectively.

EDTA plasma samples were collected from the study participants before treatment initiation (week 0) and at weeks 12, 24, and 48. The samples were centrifuged at 1500 g. Each sample was frozen at −80 °C after collection, then thawed and diluted one-quarter in TBS (10 mM Tris, 145 mM NaCl, pH 7.4) prior to measurements of complement LP proteins. HLA-B27 and CRP were determined routinely.

Immunoassays. Immunoassays were used to measure the LP proteins MBL, H-ficolin, L- ficolin, M-ficolin, collectin liver 1 (CL-L1), MASP-1, MASP-2, MASP-3, MBL-associated protein 19 (MAp19), and MAp44. All proteins, except for L-ficolin (measured using a commercial enzyme-linked immunosorbent assay [Hycult Biotechnology]), were measured by time-resolved immunofluorometric assays (TRIFMAs). The specific antibodies used in TRIFMAs were developed and produced in-house. The assays have been described in detail elsewhere.28-35 Sample dilution and loading on microtiter plates were automated using a pipetting robot (JANUS, PerkinElmer). All analyses were performed in duplicate. Measurements were repeated if the duplicate analysis’ coefficient of variation (CV) was > 15%. Interassay CV based on internal controls was also determined for each protein (all CVs were below 15%). Protein measurements were performed blinded to patient data.

Statistics. Patient demographics were assessed by median (IQR) for continuous variables and by n (%) for categorical variables. Continuous variables were compared by Kruskal-Wallis test for the MICSA cohort and Mann-Whitney U test for the DANISH cohort, respectively. Categorical variables were compared by chi-square test. LP levels in the 3 patient groups in the MICSA cohort were compared by Kruskal-Wallis test and further posthoc analyses by Dunn test. LP protein levels in the DANISH cohort were analyzed using a mixed-effects model with treatment and study week as fixed effects and patient as random effect. An unstructured residual variance-covariance matrix was included in order to allow for different SDs at different study weeks and varying correlations for different pairs of weeks. Model validation was performed by inspecting plots of standardized values against fitted values and quantile-quantile plots of standardized residuals. Correlation analyses in the DANISH cohort were assessed by Spearman correlation for LP protein levels and disease activity, functional impairment, and imaging findings, respectively.

All tests were 2-sided. P values < 0.05 were defined as significant. All statistical analyses were performed using Stata 17 software (StataCorp). Graphical representations were performed using GraphPad Prism 14 software (GraphPad Software).

Ethics. The study was approved by the Regional Scientific Ethics Committee of Central Region Denmark (1-10-72-337-18) and the Danish Data Protection Agency (1-16-02-186-20), and conducted following the Declaration of Helsinki II. Written informed consent was obtained before inclusion from all participants in the MICSA and DANISH cohorts.

RESULTS

MICSA cohort. The demographics of the patients in the MICSA cohort are shown in Table 1. Median age was 32-33 years in all 3 patient groups. The prevalence of sex differed significantly between the 3 patient groups, as only 43% of patients with axSpA were male, compared with 67% of the uLBP + SpA features group and 41% of the uLBP – SpA features group.

View this table:
Table 1.

Patient characteristics in the MICSA cohort.

The prevalence of HLA-B27 positivity differed in the 3 groups, with 74% of patients with axSpA, 20% of the uLBP + SpA features group with ≥ 1 SpA features as defined by ASAS 2009 criteria, and 8% of the uLBP – SpA features group reporting HLA positivity. The prevalence of a positive MRI according to ASAS 2009 criteria was 96% and 82% in patients with axSpA and in the uLBP + SpA features group, respectively, and did not differ significantly between the groups. Prevalence of elevated CRP (defined as > 6 mg/L) did not differ between patients in the axSpA and the uLBP + SpA features group. The newly diagnosed patients with axSpA were characterized by high disease activity (defined as Ankylosing Spondylitis Disease Activity Score [ASDAS]-CRP ≥ 2.1), and median ASDAS-CRP was 2.5.

Baseline LP protein levels. Complement LP protein plasma levels of L-ficolin, M-ficolin, and CL-L1 differed significantly in the 3 patient groups in the MICSA cohort. In contrast, H-ficolin did not differ in the 3 patient groups (Figure 1). Posthoc analyses by Dunn test showed that both L-ficolin and M-ficolin levels were increased in patients with axSpA compared to either of the 2 control groups but did not differ between the control groups. CL-L1 was significantly elevated in patients with axSpA compared with patients in the uLBP – SpA features group, and in the uLBP + SpA features group compared with the uLBP – SpA features group. However, the plasma levels of CL-L1 did not differ significantly between patients with axSpA and those in the uLBP + SpA features group. MBL, MASP-1, MASP-2, MASP-3, MAp19, and MAp44 did not differ significantly in the patient groups (Supplementary Figure S1, available with the online version of this article).

Figure 1.
Figure 1.

Plasma levels of H-ficolin, L-ficolin, M-ficolin, and CL-L1 in patients with axSpA, patients with uLBP with ≥ 1 SpA features or MRI suggestive of axSpA (uLBP + SpA features), and patients without SpA features or MRI suggestive of axSpA (uLBP – SpA features). Median and IQR are shown in plots. All 3 groups were compared by Kruskall-Wallis test (all P ≤ 0.03) and posthoc analyses with Dunn test. * P < 0.05. ** P ≤ 0.01. *** P ≤ 0.001. axSpA: axial spondyloarthritis; CL-L1: collectin liver 1; ns: not significant; uLBP: unspecific low back pain; SpA: spondyloarthritis.

DANISH cohort. The demographics of the patients in the DANISH cohort are shown in Table 2. No significant differences were observed in the 2 treatment groups. Briefly, median age was approximately 40 years, and 75-80% of patients were male. The majority of the patients fulfilled the mNY criteria, and the median disease duration was 10-12 years. Patients were included based on BASDAI scores > 4, and median disease activity measured by BASDAI and ASDAS-CRP were 5.9-6.2 and 3.1, respectively.

View this table:
Table 2.

Patient characteristics in the DANISH cohort at baseline.

Changes in LP protein levels. Complement LP protein plasma levels of L-ficolin and M-ficolin changed significantly in the 2 treatment groups from week 0 to week 12 after initiating either ADA or placebo (Figure 2). L-ficolin and M-ficolin decreased in patients treated with TNFi compared with placebo, and the percentage of the changes between week 0 and week 12 are shown in Figure 2D and Figure 2E. Plasma levels of CL-L1 did not change significantly. Plasma levels of MBL and MAp19 also changed significantly in the 2 patient groups after treatment initiation (Supplementary Figure S2, available with the online version of this article). No differences were observed for H-ficolin, MASP-2, MASP-3, and MAp44 (Supplementary Figure S2). The changes in LP protein plasma levels for each participant are shown in Supplementary Figure S3.

Figure 2.
Figure 2.

A-C: Plasma levels of lectin pathway proteins L-ficolin, M-ficolin, and CL-L1 during weeks 0-48 in the 2 treatment groups in the DANISH cohort. Means and SDs are shown in graphs. Significant changes from week 0 to week 12 are indicated with clamps. D-E: Percentage change from baseline levels between week 0 and week 12. * P < 0.05. ** P ≤ 0.01. CL-L1: collectin liver 1; DANISH: Danish Multicenter Study of Adalimumab in Spondyloarthritis.

Correlations with clinical data. Spearman correlations with clinical data (ie, measurements of ASDAS-CRP, BASDAI, and Bath Ankylosing Spondylitis Functional Index [BASFI]) were determined for L-ficolin and M-ficolin, as these protein plasma levels were found to be significantly altered in both the MICSA and DANISH cohorts. Baseline plasma levels of L-ficolin correlated negatively with baseline BASDAI, and no significant correlations between baseline plasma levels and changes in clinical scores (ASDAS-CRP, BASDAI, or BASFI) from week 0 to week 48 were observed (Table 3). Baseline M-ficolin levels correlated positively with ASDAS-CRP and BASFI, and no significant correlations between baseline plasma levels and changes in clinical scores (ASDAS-CRP, BASDAI, or BASFI) from week 0 to week 48 were observed.

View this table:
Table 3.

Spearman correlations between baseline L-ficolin and M-ficolin levels and clinical variables, and changes in clinical scores from week 0 to 48.

Correlations with imaging data. Spearman correlations with imaging data (ie, bone marrow edema, fatty lesions, erosions, SPARCC, and mSASSS) were also determined for L-ficolin and M-ficolin (Table 4). No significant correlations were observed between baseline plasma L-ficolin levels and imaging findings, but baseline L-ficolin levels correlated positively with changes in SPARCC score from baseline to week 48. Baseline M-ficolin levels correlated negatively with the extent of fatty lesions, but no significant correlations with changes from week 0 to week 48 were observed.

View this table:
Table 4.

Spearman correlations between baseline L-ficolin and M-ficolin levels and imaging findings, and changes from week 0 to 48.

DISCUSSION

The present study investigated complement LP proteins in a cross-sectional clinical cohort of patients suffering from LBP, including newly diagnosed patients with axSpA and patients with uLBP with and without SpA features, and an RCT follow-up cohort of patients with axSpA starting treatment with ADA.

Our data show increased levels of complement LP proteins L-ficolin and M-ficolin in newly diagnosed patients with axSpA compared with patients in either the uLBP + SpA features or uLBP – SpA features group. L-ficolin and M-ficolin are well-established activators of the complement system through the LP.30 The recognition of a fitting molecular structure can thus lead to downstream complement activation, causing clearing of unwanted structures (eg, microorganisms, cellular debris, or apoptotic cells) by opsonization for phagocytosis or direct killing through assembling of the terminal complement complex (membrane attack complex [MAC]), and thus releasing potent anaphylatoxins (ie, C3a, C5a). The elevated levels of the 2 ficolins partly support the results of our previous investigations of complement proteins in patients with axSpA compared with healthy blood donors, where H-ficolin and L-ficolin were elevated in patients with axSpA and showed a diagnostic potential in combination with HLA-B27.7 However, H-ficolin was not elevated in this clinical cross-sectional cohort of newly diagnosed patients with axSpA, and M-ficolin was not found to be elevated in patients with axSpA in our previous study.

Three different genes encode M-ficolin, L-ficolin, and H-ficolin: FCN1, FCN2, and FCN3, respectively. The 3 ficolins share certain physical and functional characteristics; for example, M-ficolin and L-ficolin are both localized on chromosome 9 and share 80% amino acid sequence. In contrast, H-ficolin is localized on chromosome 1 and only shares 48% amino acid sequence with the other 2 ficolins.36 However, despite similarities, the 3 ficolins differ in various aspects, such as plasma levels, tissue distribution, and ligand specificity.

L-ficolin and H-ficolin are primarily produced in the liver, whereas M-ficolin is produced mainly in monocytes and granulocytes.30 H-ficolin is the most abundant of the 3 ficolins (and of all the LP PRMs) and shows considerable interindividual variation in plasma levels.35 Further, concentrations of all 3 ficolins have been shown to display significant sex differences; L-ficolin and H-ficolin are slightly elevated in healthy males, whereas M-ficolin is slightly elevated in healthy females.35 These notions have to be taken into consideration, as the patient populations differ in our 2 studies. In our previous study, male gender and longstanding disease were more pronounced among patients with axSpA, and approximately 50% received biological treatment, potentially affecting plasma levels of LP proteins. However, despite these differences in study populations, L-ficolin was elevated in patients with axSpA in all our examined cohorts. This discovery highlights the intriguing need for further exploration of this association.

Further, all patients included in the current study were newly diagnosed, and our findings therefore support the notion that L-ficolin and M-ficolin are potential diagnostic biomarkers in axSpA diagnosis.

In addition, the current study shows new perspectives of complement proteins L-ficolin and M-ficolin in differentiating patients with axSpA from clinically relevant controls as (1) patients without axSpA but experiencing ≥ 1 SpA features defined by ASAS 2009 criteria and having a high prevalence of elevated CRP, and (2) patients with uLBP without SpA features or MRI findings suggestive of axSpA.

The use of complement proteins as early biomarkers for axSpA holds considerable appeal. However, this needs to be examined in relation to established variables such as HLA-B27, CRP, and imaging, as well as intrinsic factors related to the ficolins, since interindividual variation in plasma levels and sex differences might complicate the clinical application. Despite potential clinical limitations, a growing understanding of the disease mechanisms and the activated inflammatory pathways in axSpA may provide important understanding of the disease and further support the diagnosis. However, the diagnostic potential in axSpA was not assessed in the current study due to the limited size of the cross-sectional cohort, and this needs to be further investigated in larger cohorts of patients with axSpA and clinically relevant controls.

The follow-up RCT DANISH cohort results show plasma levels of L-ficolin and M-ficolin decrease after the initiation of ADA therapy. M-ficolin is produced by monocytes and granulocytes,30 and plasma levels are elevated during inflammatory processes (eg, various infections and autoimmune diseases such as rheumatoid arthritis [RA]).37,38 Plasma levels of M-ficolin also decreased in patients with RA after initiation of treatment with disease-modifying antirheumatic drugs, and M-ficolin levels reflect disease activity in RA determined by the Disease Activity Score in 28 joints.37 Our results show a significant correlation between M-ficolin and ASDAS-CRP (Spearman ρ 0.387, P = 0.01) but no associations with the change in ASDAS-CRP after 48 weeks of follow-up. The observed association with ASDAS-CRP might reflect associations with CRP, as no association with BASDAI was observed. However, M-ficolin also correlated positively with baseline BASFI (Spearman ρ 0.301, P = 0.04). One might speculate that elevated M-ficolin could be associated with the presence of radiographic changes—and thus disease severity experienced by patients—and expressed as higher BASFI scores. Baseline L-ficolin levels were positively associated with changes in SPARCC score from week 0 to week 48, and high levels might be associated with more severe progression of the disease. L-ficolin is mainly produced by hepatocytes and secreted into the bloodstream.39 Little is known about L-ficolin fluctuations during inflammatory processes. Other studies have found that complement activation determined by measurements of soluble MAC (sC5b-C9; also termed soluble terminal complement complex) decreases in patients with SpA (both psoriatic arthritis and radiographic axSpA) after 6 weeks of treatment with TNFi.40 Such decreases in complement activation might result from decreases in M-ficolin and L-ficolin since both are well-established activators of the complement system through the LP, but this needs further investigation in larger cohorts.

One of the major strengths of our study is the complete measurement of all 10 LP proteins in a cross-sectional cohort as well as a follow-up RCT cohort of patients with axSpA. Another strength is the well-characterized patients included in the MICSA and DANISH cohorts, especially considering the follow-up period of 3.5 years in the MICSA cohort which resulted in extensive material for diagnostic purposes. Further, dropout during follow-up in the DANISH cohort was very limited and data, including MRI scans and radiographs, were comprehensively collected during the follow-up period. However, our study also has limitations to consider. This includes the size of the study population in the MICSA cohort and the small number of patients with axSpA in the cohort (n = 23/142). Due to the size of the cohort, diagnostic potential was not assessed in the current study and further investigations of the diagnostic potential of the specific complement proteins are therefore warranted in larger cohorts including patients with axSpA and relevant controls. Further, most patients included in the DANISH cohort are HLA-B27–positive males with radiographic axSpA fulfilling the mNY criteria at baseline. Therefore, the results cannot necessarily be extrapolated to nonradiographic axSpA, which affects a higher proportion of female and HLA-B27–negative individuals.

Our findings provide new insights into the inflammatory processes in axSpA and support the involvement of the complement system in axSpA pathogenesis. Future studies should investigate the diagnostic potential of complement proteins in larger clinical cohorts and investigate changes in complement proteins related to the various treatments (ie, with different modes of action) over time in both radiographic and nonradiographic axSpA.

Footnotes

  • The study was supported by The Danish Rheumatism Association.

  • The authors declare no conflicts of interest relevant to this article.

  • Accepted for publication September 1, 2023.

REFERENCES

  1. 1.↵
    1. Sieper J,
    2. Poddubnyy D.
    Axial spondyloarthritis. Lancet 2017;390:73-84.
    OpenUrlCrossRefPubMed
  2. 2.↵
    1. Redeker I,
    2. Callhoff J,
    3. Hoffmann F, et al.
    Determinants of diagnostic delay in axial spondyloarthritis: an analysis based on linked claims and patient-reported survey data. Rheumatology 2019;58:1634-8.
    OpenUrlPubMed
  3. 3.↵
    1. Sykes MP,
    2. Doll H,
    3. SenGupta R,
    4. Gaffney K.
    Delay to diagnosis in axial spondyloarthritis: are we improving in the UK? Rheumatology 2015;54:2283-4.
    OpenUrlCrossRefPubMed
  4. 4.↵
    1. Danve A,
    2. Deodhar A.
    Treatment of axial spondyloarthritis: an update. Nat Rev Rheumatol 2022;18:205-16.
    OpenUrl
  5. 5.↵
    1. Maksymowych WP,
    2. Wichuk S,
    3. Dougados M, et al.
    Modification of structural lesions on MRI of the sacroiliac joints by etanercept in the EMBARK trial: a 12-week randomised placebo-controlled trial in patients with non-radiographic axial spondyloarthritis. Ann Rheum Dis 2018;77:78-84.
    OpenUrlAbstract/FREE Full Text
  6. 6.↵
    1. Haroon N,
    2. Inman RD,
    3. Learch TJ, et al.
    The impact of tumor necrosis factor alpha inhibitors on radiographic progression in ankylosing spondylitis. Arthritis Rheum 2013;65:2645-54.
    OpenUrlCrossRefPubMed
  7. 7.↵
    1. Troldborg A,
    2. Thiel S,
    3. Mistegaard CE, et al.
    Plasma levels of H- and L-ficolin are increased in axial spondyloarthritis: improvement of disease identification. Clin Exp Immunol 2020;199:79-87.
    OpenUrl
  8. 8.↵
    1. Ambarus C,
    2. Yeremenko N,
    3. Tak PP,
    4. Baeten D.
    Pathogenesis of spondyloarthritis: autoimmune or autoinflammatory? Curr Opin Rheumatol 2012;24:351-8.
    OpenUrlCrossRefPubMed
  9. 9.↵
    1. Mistegaard CE,
    2. Proft F.
    The complement system in spondyloarthritis: what do we know? touchREVIEWS in RMD 2022;2:50-6.
    OpenUrl
  10. 10.↵
    1. Yang C,
    2. Ding P,
    3. Wang Q, et al.
    Inhibition of complement retards ankylosing spondylitis progression. Sci Rep 2016;6:34643.
    OpenUrl
  11. 11.↵
    1. Merle NS,
    2. Church SE,
    3. Fremeaux-Bacchi V,
    4. Roumenina LT.
    Complement system Part I – Molecular mechanisms of activation and regulation. Front Immunol 2015;6:262.
    OpenUrlCrossRefPubMed
  12. 12.↵
    1. Merle NS,
    2. Noe R,
    3. Halbwachs-Mecarelli L,
    4. Fremeaux-Bacchi V,
    5. Roumenina LT.
    Complement system part II: role in immunity. Front Immunol 2015;6:257.
    OpenUrlCrossRefPubMed
  13. 13.↵
    1. Roozendaal R,
    2. Carroll MC.
    Complement receptors CD21 and CD35 in humoral immunity. Immunol Rev 2007;219:157-66.
    OpenUrlCrossRefPubMed
  14. 14.↵
    1. Ricklin D,
    2. Hajishengallis G,
    3. Yang K,
    4. Lambris JD.
    Complement: a key system for immune surveillance and homeostasis. Nat Immunol 2010;11:785-97.
    OpenUrlCrossRefPubMed
  15. 15.↵
    1. Pihl R,
    2. Jensen L,
    3. Hansen AG, et al.
    Analysis of factor D isoforms in Malpuech-Michels-Mingarelli-Carnevale patients highlights the role of MASP-3 as a maturase in the alternative pathway of complement. J Immunol 2017;199:2158-70.
    OpenUrlAbstract/FREE Full Text
  16. 16.↵
    1. Breban M,
    2. Beaufrère M,
    3. Glatigny S.
    The microbiome in spondyloarthritis. Best Pract Res Clin Rheumatol 2019;33:101495.
    OpenUrlPubMed
  17. 17.↵
    1. Hermansen LT,
    2. Loft AG,
    3. Christiansen AA, et al.
    No diagnostic utility of antibody patterns against Klebsiella pneumoniae capsular serotypes in patients with axial spondyloarthritis vs. patients with non-specific low back pain: a cross-sectional study. Scand J Rheumatol 2017;46:296-302.
    OpenUrl
  18. 18.↵
    1. Kiil RM,
    2. Mistegaard CE,
    3. Jurik AG, et al.
    Diagnosing axial spondyloarthritis by multidiciplinary team conference at 3.5 years’ follow-up in a cohort of patients with disease features according to the ASAS criteria. Scand J Rheumatol 2022;51:291-9.
    OpenUrl
  19. 19.↵
    1. Kiil RM,
    2. Mistegaard CE,
    3. Loft AG,
    4. Zejden A,
    5. Hendricks O,
    6. Jurik AG.
    Differences in topographical location of sacroiliac joint MRI lesions in patients with early axial spondyloarthritis and mechanical back pain. Arthritis Res Ther 2022;24:75.
    OpenUrl
  20. 20.↵
    1. Arnbak B,
    2. Grethe Jurik A,
    3. Hørslev-Petersen K, et al.
    Associations between spondyloarthritis features and magnetic resonance imaging findings: a cross-sectional analysis of 1,020 patients with persistent low back pain. Arthritis Rheumatol 2016;68:892-900.
    OpenUrl
  21. 21.↵
    1. Pedersen SJ,
    2. Poddubnyy D,
    3. Sørensen IJ, et al.
    Course of magnetic resonance imaging-detected inflammation and structural lesions in the sacroiliac joints of patients in the randomized, double-blind, placebo-controlled Danish multicenter study of adalimumab in spondyloarthritis, as assessed by the Berlin and spondyloarthritis research consortium of Canada methods. Arthritis Rheumatol 2016;68:418-29.
    OpenUrl
  22. 22.↵
    1. Arnbak B,
    2. Jensen TS,
    3. Egund N, et al.
    Prevalence of degenerative and spondyloarthritis-related magnetic resonance imaging findings in the spine and sacroiliac joints in patients with persistent low back pain. Eur Radiol 2016;26:1191-203.
    OpenUrlCrossRefPubMed
  23. 23.↵
    1. Maksymowych WP,
    2. Dhillon SS,
    3. Park R,
    4. Salonen D,
    5. Inman RD,
    6. Lambert RG.
    Validation of the spondyloarthritis research consortium of Canada magnetic resonance imaging spinal inflammation index: is it necessary to score the entire spine? Arthritis Rheum 2007;57:501-7.
    OpenUrlCrossRefPubMed
  24. 24.↵
    1. Maksymowych WP,
    2. Inman RD,
    3. Salonen D, et al.
    Spondyloarthritis research Consortium of Canada magnetic resonance imaging index for assessment of sacroiliac joint inflammation in ankylosing spondylitis. Arthritis Rheum 2005;53:703-9.
    OpenUrlCrossRefPubMed
  25. 25.↵
    1. Maksymowych WP,
    2. Wichuk S,
    3. Chiowchanwisawakit P,
    4. Lambert RG,
    5. Pedersen SJ.
    Development and preliminary validation of the spondyloarthritis research consortium of Canada magnetic resonance imaging sacroiliac joint structural score. J Rheumatol 2015;42:79-86.
    OpenUrlAbstract/FREE Full Text
  26. 26.↵
    1. Krabbe S,
    2. Østergaard M,
    3. Pedersen SJ, et al.
    Canada—Denmark MRI scoring system of the spine in patients with axial spondyloarthritis: updated definitions, scoring rules and inter-reader reliability in a multiple reader setting. RMD Open 2019;5:e001057.
    OpenUrlAbstract/FREE Full Text
  27. 27.↵
    1. Krabbe S,
    2. Sørensen IJ,
    3. Jensen B, et al.
    Inflammatory and structural changes in vertebral bodies and posterior elements of the spine in axial spondyloarthritis: construct validity, responsiveness and discriminatory ability of the anatomy-based CANDEN scoring system in a randomised placebo-controlled trial. RMD Open 2018;4:e000624.
    OpenUrlAbstract/FREE Full Text
  28. 28.↵
    1. Thiel S,
    2. Møller-Kristensen M,
    3. Jensen L,
    4. Jensenius JC.
    Assays for the functional activity of the mannan-binding lectin pathway of complement activation. Immunobiology 2002;205:446-54.
    OpenUrlCrossRefPubMed
  29. 29.
    1. Krarup A,
    2. Sørensen UB,
    3. Matsushita M,
    4. Jensenius JC,
    5. Thiel S.
    Effect of capsulation of opportunistic pathogenic bacteria on binding of the pattern recognition molecules mannan-binding lectin, L-ficolin, and H-ficolin. Infect Immun 2005;73:1052-60.
    OpenUrlAbstract/FREE Full Text
  30. 30.↵
    1. Wittenborn T,
    2. Thiel S,
    3. Jensen L,
    4. Nielsen HJ,
    5. Jensenius JC.
    Characteristics and biological variations of M-ficolin, a pattern recognition molecule, in plasma. J Innate Immun 2010;2:167-80.
    OpenUrlCrossRefPubMed
  31. 31.
    1. Axelgaard E,
    2. Jensen L,
    3. Dyrlund TF, et al.
    Investigations on collectin liver 1. J Biol Chem 2013;288:23407-20.
    OpenUrlAbstract/FREE Full Text
  32. 32.
    1. Degn SE,
    2. Jensen L,
    3. Gál P, et al.
    Biological variations of MASP-3 and MAp44, two splice products of the MASP1 gene involved in regulation of the complement system. J Immunol Methods 2010;361:37-50.
    OpenUrlCrossRefPubMed
  33. 33.
    1. Møller-Kristensen M,
    2. Jensenius JC,
    3. Jensen L, et al.
    Levels of mannan-binding lectin-associated serine protease-2 in healthy individuals. J Immunol Methods 2003;282:159-67.
    OpenUrlCrossRefPubMed
  34. 34.
    1. Degn SE,
    2. Thiel S,
    3. Nielsen O,
    4. Hansen AG,
    5. Steffensen R,
    6. Jensenius JC.
    MAp19, the alternative splice product of the MASP2 gene. J Immunol Methods 2011;373:89-101.
    OpenUrlCrossRefPubMed
  35. 35.↵
    1. Troldborg A,
    2. Hansen A,
    3. Hansen SW,
    4. Jensenius JC,
    5. Stengaard-Pedersen K,
    6. Thiel S.
    Lectin complement pathway proteins in healthy individuals. Clin Exp Immunol 2017; 188:138-47.
    OpenUrlCrossRef
  36. 36.↵
    1. Garred P,
    2. Honoré C,
    3. Ma YJ, et al.
    The genetics of ficolins. J Innate Immun 2010;2:3-16.
    OpenUrlCrossRefPubMed
  37. 37.↵
    1. Ammitzbøll CG,
    2. Thiel S,
    3. Jensenius JC, et al.
    M-ficolin levels reflect disease activity and predict remission in early rheumatoid arthritis. Arthritis Rheum 2013;65:3045-50.
    OpenUrlCrossRefPubMed
  38. 38.↵
    1. Jørgensen CM,
    2. Jensen L,
    3. Christiansen M,
    4. Bjerre M,
    5. Jensen JMB,
    6. Thiel S.
    Pattern recognition molecules of the lectin pathway-screening of patients with suspected immunodeficiency. J Clin Immunol 2019;39:668-77.
    OpenUrl
  39. 39.↵
    1. Holmskov U,
    2. Thiel S,
    3. Jensenius JC.
    Collections and ficolins: humoral lectins of the innate immune defense. Annu Rev Immunol 2003;21:547-78.
    OpenUrlCrossRefPubMed
  40. 40.↵
    1. Hokstad I,
    2. Deyab G,
    3. Wang Fagerland M, et al.
    Tumor necrosis factor inhibitors are associated with reduced complement activation in spondylarthropathies: an observational study. PLoS One 2019;14:e0220079.
    OpenUrl

DATA AVAILABILITY

The data underlying this article will be shared on reasonable request to the corresponding author.

Back to top

In this issue

Print
Download PDF
Article Alerts
Email Article
Citation Tools

 Request Permissions

Bookmark this article

Jump to section

Keywords

AXIAL SPONDYLOARTHRITIS
mannose-binding lectin complement pathway
TUMOR NECROSIS FACTOR INHIBITORS

Keywords