ENGAGEMENT OF CD45 DURING IN-VITRO PRIMING ENHANCES ANTIGEN-SPECIFIC T-H CELL FREQUENCIES

CD45 is a transmembrane protein tyrosine phosphatase expressed by all lymphoid cells including T cells, Substantial experimental data has sh own that CD45 maintains a permissive state for TCR signaling, The high ly glycosylated extracellular domain of CD45 may be the site of intera ction with regulatory lectin-like counter-receptors on antigen-present ing cells, The mAb NDA5, recognizing a unique but broadly distributed epitope of CD45, was used to study the possible immunoregulatory role of CD45 during anti-CD3 and antigen-specific CD4(+) T cell activation, In vitro priming of peripheral blood mononuclear cells with peptide a ntigens in the presence of mAb NDA5 results in a higher frequency of a ntigen-specific T cells. The responses of both naive and memory T cell s to peptide antigens were sensitive to mAb NDA5-enhanced priming, Ant i-CD3 activation of normal resting T cells, in the presence of mAb NDA 5, resulted in enhancement of tyrosine phosphorylation of specific int racellular proteins associated with TCR signal transduction. In cultur es without antigen, mAb NDA5 down-regulated the cell surface expressio n of both CD3 and CD4, yet did not stimulate proliferation of resting T cells, Together these results suggest that engagement of CD45 during in vitro priming has a significant effect on the development of antig en-specific T cell populations.