Alteration of sialyl Lewis epitope expression in pterygium

PURPOSE. Mucin-related antigens are abundantly expressed by the cells of th e normal human conjunctiva. The pattern of these antigens in pterygium, and especially the role of Gal beta 1-3GlcNAc alpha 2,3-sialyltransferase (ST3 Gal III), sialyltransferase necessary to build the sialyl-Le(a) (Lewis(a)) antigen, were studied. METHODS. Immunoperoxidase staining was performed on 28 pterygia using diffe rent monoclonal antibodies: anti-M1 (against the peptidic core of gastric m ucins encoded by MUC 5AC gene), anti-Le(a) (7LE), anti-sialyl Le(a) (NS 19- 9), and anti-Le(b) (2-25LE). A serologic Lewis determination was done in 18 patients. ST3Gal III sialyltransferase expression was also studied in 10 h ealthy conjunc tiva and 10 pterygia by reverse transcriptase-polymerase cha in reaction (RT-PCR). Glyceraldehyde-3-phosphate-dehydrogenase was used as an endogenous internal control. RESULTS. First, Le(a), sialyl Le(a), and Le(b) immunoreactivities either de creased or were no longer detectable in pterygium goblet cells as opposed t o normal conjunctiva. Second, unlike in pterygium, the Lewis immunoreactivi ty, which is mainly located in the surface epithelial cells in the normal c onjunctiva, was occasionally restricted to the epithelial cells of the deep layers. However, M1 mucins did show an identical pattern expression in a n ormal conjunctiva and pterygium. ST3Gal III expression was significantly lo wer in pterygium (0.20 +/- 0.02 AU [arbitrary units]) than in normal conjun ctiva (0.95 +/- 0.12 AU). CONCLUSIONS. ST3Gal III gene is less expressed in pterygium than in normal conjunctiva. This observation could explain the decrease of sialyl Le(a) ex pression observed in pterygium by immunohistology.