EXPRESSION OF THE SIALOSYL-TN EPITOPE ON CD45 DERIVED FROM ACTIVATED PERIPHERAL-BLOOD T-CELLS

The cell surface protein tyrosine phosphatase CD45 is a major target o f IgM anti-T cell autoantibodies in systemic lupus erythematosus (SLE) . The autoreactive determinants on CD45 are O-linked glycans expressed on activated T cells and certain T cell lines, rather than linear or conformational polypeptide epitopes or N-linked glycans. To identify o ligosaccharide structures that may play a role in the functional inter actions of CD45 or are candidate target epitopes of SLE anti-CD45 auto antibodies, autoreactive CD45 purified from Jurkat T cells and non-aut oreactive CD45 purified from CLL B cells were tested by ELISA for expr ession of mucin-type O-glycan structures. Monoclonal antibodies (mAbs) directed against blood group A, type 1 H chains, type 2 H chains, T, Le(a), sialylated-lee, Leb, sialylawted-Le(c), Lex, sialylated-Le(x), multi-fucosylated Le(x), Le(y), and sialylated-extended Le(y) failed t o react with CD45 from either B cells or T cells. However, mAbs direct ed against Tn (galNAc alpha 1-O-ser/thr) or sialosyl-Tn (neuNAc alpha 2-GgalNAc alpha 1-O-ser/thr) structures reacted with CD45 derived from Jurkat T cells, but not from CLL B cells. Anti-Tn mAbs also reacted i n western blotting procedures with CD45 isolated from Jurkat T cells, but did not react with CD45 isolated from GEM, MOLT-3, or PEER T cells ; Daudi, Raji, or CLL B cells; or resting or Con A-activated PBL. Howe ver, anti-sialosyl-Tn mAbs stained blots of CD45 isolated from Jurkat and CEM T cells and Con A-activated PBL, a pattern of reactivity simil ar to that of the anti-CD45 autoantibodies. Flow cytometric analyses d emonstrated that the sialosyl-Tn epitopes are expressed on a subpopula tion of CD4+/CD8- T cells.