Enhancement of the Affinity of Glucocorticoid Receptors as a Mechanism Underlying the Steroid-sparing Effect of Intravenous Immunoglobulin

To the Editor:

Intravenous immunoglobulin (IVIG) is commonly used for the treatment of a wide range of autoimmune diseases^1,2,3. The available data also suggest that IVIG has a steroid-sparing effect: either enhancing the steroid sensitivity or reducing the steroid dose^4,5,6. These reports indicate that IVIG can be considered as a therapeutic choice in steroid-resistant autoimmune and inflammatory diseases such as dermatomyositis, asthma, and polymyositis. We aimed to identify the underlying molecular mechanisms by which IVIG therapy can restore steroid sensitivity and can as a “steroid-sparing” agent.

We addressed the steroid-sparing effect of IVIG by analyzing the affinity of glucocorticoid receptor (GCR) using lymphoblastoid cell line CEM-C1. CEM-C1 is resistant to steroids despite its expression of functional GCR⁷ and hence represents an apposite model to study the steroid-sparing effect of IVIG.

Octagam^® (Octapharma, Lingolsheim, France) was used as a source of IVIG in all the experiments. GCR-binding affinity was determined by [³H]-dexamethasone ([³H]-Dex) radioligand binding assays and Scatchard analysis⁸. The cells were incubated with increasing concentrations of [³H]-dexamethasone (Amersham Corp., Arlington Heights, IL, USA; range 0.1–50 nM) in the presence or absence of 500-fold excess of nonlabeled dexamethasone (Sigma Chemical Co., St. Louis, MO, USA) for 60 min. After incubation, the cells were rinsed, lysed, and counted in a ß-counter.

Pretreatment of CEM-C1 cells with IVIG followed by dexamethasone (10 μM) led to an increase in apoptosis as compared to dexamethasone alone. We thus assessed whether this increase in sensitivity of CEM-C1 to dexamethasone was due to the changes in GCR-binding affinity during IVIG treatment. The baseline GCR dissociation constant (Kd) of CEM-C1 was at 7.36 nM level. Interestingly, after 2 h of IVIG treatment of cells, the mean Kd had significantly fallen to 3.12 nM (Figure 1), suggesting an enhancement of affinity for GCR by IVIG.

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Figure 1.

Scatchard analysis of [³H]-dexamethasone radioligand binding data of CEM-1 cells. Black triangles represent cells treated with 0.24 mM IVIG for 2 h.

Longterm steroid use is associated with many debilitating adverse effects and hence several alternative steroid-sparing agents including cyclosporine and mepolizumab have been used^9,10. Many of these alternative treatments, such as cyclosporine, also have potentially harmful adverse effects. IVIG therapy has been reported to have steroid-sparing effects with relatively few adverse effects. The mechanisms involved in steroid-sparing effects of IVIG are not fully understood but may involve immunomodulation. Using a steroid-resistant CEM-C1 cell model, our results suggest that one of the steroid-sparing effects of IVIG is mediated through the improved GCR-binding affinity.