The inhibition of T cell proliferative responses by crosslinking CD7 and IgM-Fc receptors.

Previous work from our laboratory described a human T cell soluble ligand that inhibited T cell proliferative responses to mitogen and alloantigen by interacting with CD7 and/or the receptor for the IgM-Fc portion (FcR mu) on T cells. In this report, we used mouse anti-human CD7 monoclonal antibodies (mAb) and purified human IgM (HIgM) to substitute for the human ligand and examined the possible involvement of these receptors in the inhibition of T cell proliferation. Preincubation of human T cells with mouse anti-CD7 mAb, HIgM, mouse anti-human IgM (MAH IgM) alone, or any of these combinations as a primary antibody did not inhibit mitogen- or alloantigen-induced T cell replication. Similar effects were seen with the pretreatment of T cells with an irrelevant negative control primary mAb or a secondary-step goat anti-mouse immunoglobulin (GAM Ig), goat anti-human IgM-Fc (GAH Fc mu), or both. In contrast, the pretreatment of T cells with anti-CD7 and/or HIgM followed by the appropriate secondary-step crosslinking antibody significantly reduced their proliferative responses to mitogen and alloantigen. Similarly, crosslinking of CD7 and FcR mu on human transformed T cell lines inhibited their spontaneous proliferation. The inhibitory effect of crosslinking CD7 and FcR mu was not due to cytotoxic effects of these antibodies and appears to be temperature sensitive. These findings suggest that crosslinking CD7 and/or FcR mu appears to have a novel role in down-regulating T cell proliferation.