3H11, a unique cell surface molecule involved in the function of the CD45RA+ subset of CD4+ cells

We have developed a mAb anti-3H11 by immunizing mice with a T cell line derived from the Callithrix jacchus (common marmoset). Anti-3H11 is reactive with approximately 48% of unfractionated T cells, 62% of CD4+ cells and 39% of CD8+ cells. Among CD4 cells, anti-3H11 preferentially reacts with the CD45RA+ T cell subset. The majority of helper activity for pokeweed mitogen (PWM)-driven B cell IgG synthesis and T cell response to recall antigen such as tetanus toxoid was found within the 3H11-CD4 cell population, whereas anti-3H11+CD4+ cells provided poor helper function for PWM-driven B cell IgG synthesis and were more responsive to concanavalin A and autologous mixed lymphocyte reaction. Biochemical characterization showed that anti-3H11 precipitated a single protein band with a relative molecular weight of 32,000 from 125I-surface labeled cell lysate. Biochemical, phenotypic and functional studies revealed that the 3H11 molecule appeared to be different from previously established molecules on the T cell surface. Interestingly, addition of anti-3H11 to the combination of CD4 and B cells in the presence of CD8 cells but not to the combination of CD4 and B cells resulted in enhancement of the suppression of PWM-driven B cell IgG synthesis. Moreover, anti-3H11 had a co-mitogenic effect on T cells via the CD2 and CD3 pathways, and this co-mitogenic activity is restricted to the CD45RA+ T cells. Taken together, our results show that the 3H11 molecule is a novel antigen which may play an important role in the activation and function of the CD45RA+ subset of T cells.