Quantitative analysis of lacrimal gland function, apoptotic figures, Fas and Fas ligand expression of lacrimal glands in dry eye patients
Introduction
Various disease mechanisms may account for dry eye syndrome, including decreased blink rate, shortened tear break-up time or delayed tear clearance; all of which are not directly related to lacrimal gland dysfunction (Tseng and Tsubota, 1997). However, in Sjögren's syndrome (SS), severe lacrimal gland dysfunction is the key mechanism (Pflugfelder et al., 1993, Tsubota et al., 1996, Xu et al., 1996). We have previously reported that these types of dry eye have lymphocytic infiltration into the lacrimal gland accompanied by some acinar cell destruction, resulting in dramatic dysfunction of the lacrimal gland (Xu et al., 1996). Reflex tear production is lost, even with strong stimulation such as nasal stimulation, as is basic secretion (Tsubota et al., 1996, Tsubota et al., 1999a). In this situation, essential tear components cannot reach the ocular surface epithelium, and the epithelium may develop squamous metaplasia (Tseng, 1985, Tsubota, 1998, Tsubota et al., 1999b).
A mysterious feature of the lacrimal gland in SS is the presence of some intact-looking acinar cells remaining in the lacrimal gland, even though lacrimal gland function is almost totally lost. We have proposed that these normal-looking acinar cells in SS are in the early phase of apoptosis and cannot function (Fujihara et al., 1999, Tsubota et al., 2000). This concept can explain the difference in lacrimal gland function between SS and SS with enlarged exocrine glands; both of which have massive lymphocyte infiltration. Whereas, SS shows a lot of apoptotic figures in the lacrimal gland, there are almost no apoptotic figures in the lacrimal gland in patients with SS with enlarged exocrine glands and non-Sjögren's syndrome-type dry eye (Fujihara et al., 1999, Tsubota et al., 2000). In the animal model of SS, we also showed the importance of apoptosis in acinar cells for the destruction of exocrine glands (Saito et al., 1999). Thus, we now are able to hypothesize that lacrimal gland function is related to the apoptotic process in lacrimal gland acinar cells. Furthermore, apoptosis may be related to the Fas and Fas ligand (FasL) interaction. In this paper, we have quantitatively compared lacrimal gland function (Schirmer test result) and apoptosis, and Fas and FasL expression of lacrimal gland acinar cells. As expected, there was a correlation between function and the number of apoptotic figures in the lacrimal gland, and with FasL expression in infiltrating lymphocytes.
Section snippets
Diagnosis of Sjögren's syndrome and dry eye
The diagnosis of SS was made by a modification of proposed criteria of Fox et al. (1986); (1) objective evidence of keratoconjunctivitis sicca, as documented by Rose Bengal or fluorescein dye staining, (2) objective evidence of diminished salivary gland flow, (3) minor salivary gland biopsy, obtained through normal mucosa, where the specimen contains at least four evaluative salivary gland lobules, and having an average of at least 2 foci/4 mm2 or positive lymphocyte infiltration of lacrimal
Results
In SS lacrimal glands, some acinar cells were clearly stained by APO2·7 antibody indicating the early phase of apoptosis (Fig. 1(a) and (b)). This antibody reacts with the mitochondria protein induced in the early phase of apoptosis (Zhang et al., 1996), and was shown to stain identical cells, which were stained by the TUNEL method (Fujihara et al., 1999). It was shown that this antibody is a useful and early marker for apoptosis, not only in hemopoietic cells but also in epithelial cells (
Discussion
This paper shows a correlation between the presence of apoptotic figures in lacrimal glands and gland function. There was a further correlation between lacrimal gland function and FasL expression, which suggests that the Fas–FasL interaction is an important mechanism in lacrimal gland dysfunction, which is probably mediated via infiltrating lymphocytes.
Tear function was correlated with lacrimal gland apoptosis. This result suggests that normal-looking acinar cells in SS are already in an early
Acknowledgements
A grant from the High Tech Research Center of Tokyo Dental College, Chiba, Japan and an award from the Medical School Faculty and Alumni Grants of Keio University Medical Science Fund, Tokyo, Japan, supported this study.
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