Role of a nonimmunoglobulin cell surface determinant in the activation of B lymphocytes by thymus-independent antigens.

Abstract

Lyb 5 is a b[bone marrow-derived]-cell alloantigen which is expressed on 50-60% of B cells. It was defined originally on the basis of cytotoxicity. A new reactivity was described within the anti-Lyb 5 serum based on selective inhibition of antibody responses in vitro by this antiserum without complement. This inhibitory activity of anti-Lyb 5.1 serum appeared to be due to recognition of antigenic determinants different from the prototype antigens detected in the cytotoxicity assay. Anti-Lyb 5 serum incorporated into spleen cell cultures selectively inhibited antibody responses to a class of thymus-independent antigens (TI-2) previously characterized by their failure to elicit antibody formation in immature mice or in the defective CBA/N strain. Responses to optimal concentrations of TI-1 antigens, which can induce antibody synthesis in these mice, were unaffected by the addition of anti-Lyb 5.1 serum. The B cell alloantigen defined by this functional assay was designated tentatively Lyb 7, and it was distinct from cell surface immunoglobulins. Lyb 7 appeared to have a role in the activation of B lymphocytes by the TI-2 class of thymus-independent antigens.