T lymphocyte-dependent B lymphocyte proliferative response to antigen. II. Induction of polyclonal B lymphocyte activation of normal B cells and of Lyb-5- B cells from xid mice via recognition of self-IA antigens

Abstract

We extended our investigations into the genetic requirements and antigen dependence for the induction of polyclonal B lymphocyte proliferation by primed T lymphocytes. By using recombinant inbred mouse strains and antigen-specific T lymphocyte clones that lack alloreactivity, the genetic requirement was mapped to the IA subregion of the MHC. Furthermore, approaches that prevented or limited the accessibility of antigens to the B lymphocyte surface demonstrated that antigen binding onto the B lymphocyte surface was probably not necessary for induction of B lymphocyte proliferation. These experiments suggest strongly that T lymphocyte recognition of B lymphocyte Ia molecules in the absence of sIg cross-linking or in the absence of antigen bound nonspecifically to B lymphocytes can cause cellular activation. Similar T lymphocyte-dependent B lymphocyte activation was seen when Lyb-5- cells from CBA/N mice with the xid defect were cultured. Increases in the number of cells secreting immunoglobulins could be detected in the proliferating B lymphocyte cultures, suggesting that the culture conditions had fulfilled the requirements for B lymphocyte differentiation into antibody-producing cells. Although anti-Ig did not interfere with the B lymphocyte proliferative responses, it did diminish the number of cells secreting immunoglobulins. The implications of these experiments in extending our understanding of the activation pathway of Lyb-5- and Lyb-5+ B lymphocytes are discussed.