Analysis of B Cell Immediate Early Gene Expression in Response to Contact Dependent T Cell Help and Anti-immunoglobulins: a Thesis

Abstract

B cells get help in the antibody response by presenting processed antigen to helper T cells. We asked whether the antigen presenting B cell must induce T helper functions before receiving help, or whether B cell activation is a direct consequence of T cell antigen recognition on the B cell surface. Although antigen-dependent increases in B cell c-myc expression occur as early as two hours after conjugation, the B cell response depends on induction of a contact-dependent helper function in the T cell, which is inhibitable by cyclosporin A. Induction but not delivery of contact help is blocked by anti-class II MHC antibody, indicating that the delivery of T cell help is not Ag dependent or MHC restricted. Also, contact with activated helper T cells induces a different pattern of immediate early gene expression from signals transduced through the B cell antigen receptor. Egr-1 is rapidly upregulated in response to mitogenic signals induced by receptor crosslinking on murine B lymphocytes, and its expression closely correlates with B cell proliferation in several models of B cell activation and tolerance. We compared egr-1 expression during B cell stimulation with Fab'2 and IgG anti-Ig, since it is known that Fab'2 anti-Ig is mitogenic while IgG is not, due to a dominant inhibitory effect of crosslinking the B cell FcγRII to membrane Ig. While mitogenic doses of Fab'2 anti-Ig induce large and rapid increases in egr-1 expression, intact anti-Ig results in only small increases in egr-1 mRNA, comparable to that seen with submitogenic concentrations of Fab'2 anti-Ig. However, when IL-4 is added as a comitogen to induce B cell proliferation with submitogenic concentrations of Fab'2 anti-Ig or IgG anti-Ig, no concomitant increases in egr-1 are observed. The regulation of egr-1 therefore, is similar to that of c-myc in this system, since neither correlates with IL-4 induced DNA synthesis.