EXPRESSION OF N-ACETYL-D-GALACTOSAMINE ASSOCIATED EPITOPE IN SYNOVIUM- A POTENTIAL MARKER OF GLYCOPROTEIN PRODUCTION

Objective. To investigate synovial glycoprotein production in situ, a novel monoclonal antibody (Mab), A13D8, was used to evaluate the expre ssion of an epitope containing N-acetyl-D-galactosamine (Ga1NAc) in no rmal and pathological synovium. Methods. Immunohistological and cytoch emical analysis of synovial tissue samples was undertaken with single and double staining techniques using the A13D8 Mab, anti-CD68, vascula r cell adhesion molecule-1 (VCAM-1), the hyaluronan associated enzyme uridine diphosphoglucose dehydrogenase (UDPGD), and the anti-Golgi Mab SSN/HR-1992. The specificity of the A13D8 Mab was established through blocking studies using carbohydrate residues, including Ga1NAc and N- acetly-glucosamine (G1cNAc). Results. A13D8 is expressed intensely in the cytoplasm of normal type B lining cells, which coexpress VCAM-1 an d UDPGD, and is not expressed by CD68+ type A lining cells. In the lin ing layer of RA synovium, there is a negative correlation between A13D 8 expression and the level of lymphocytic infiltration in the sublinin g areas (r = -0.43, p < 0.001). The endothelium of a subset of venules , typically in lymphocyte-rich aggregates, also stains intensely for A 13D8. Pretreatment of the Mab with Ga1NAc completely eliminates the ti ssue staining, as well as the 110 kDa band seen on immunoblot, whereas pretreatment of A13D8 with G1cNAc and lactose has no effect. Double s taining of HEp-2 cells with A13D8 and the anti-Golgi Mab SSN/HR-1992 r eveals co-localization of the A13D8 epitope to the Golgi apparatus. Co nclusion. Type B synovial lining cells and selected synovial endotheli um express Ga1NAc containing epitope identified by Mab A13D8. Marked r eduction in the expression of this epitope in the lining layer of infl amed RA synovium suggests that the synovial production of Ga1NAc conta ining glycoproteins, such as mucins, may be altered in this disorder.