Collaboration of allogeneic T and B lymphocytes in the primary antibody response to sheep erythrocytes in vitro

Abstract

This study provides a direct quantitative comparison of the helper effects of allogeneic and syngeneic rat T cells in the production of direct SRBC plaque forming cell (PFC) responses by B cells in culture. In syngeneic T B combinations, log log plots of the number of PFC generated after 5.5 days in culture vs. the number of T cells employed as helpers showed a linear response between 104 and 2.5 x 105 T cells added. Allogeneic T B combinations, in which the T cells possess the capacity for reactivity to major alloantigens of the B cell donor, showed a different dose/response relationship in which PFC responses were decreased at high T/B ratios and augmented at low T/B ratios. In this system, responses were detected with as few as 103 allogeneic T cells. Use of negatively selected allogeneic T populations, specifically depleted of mixed lymphocyte interaction (MLI) and graft vs. host reactivity for B cell alloantigens, as helpers gave dose/response curves quantitatively identical to responses with syngeneic T B combinations and also with F1 T cell parental B cell combinations. These data indicate that rat T and B cells need not share a major histocompatibility complex haplotype in order to collaborate effectively in a primary direct PFC response to SRBC in culture. In addition, the PFC response required the combined presence of T and B cells as well as antigen in the cultures, a finding consistent with the two signal model of B cell activation. Finally, the dose/response data obtained suggest the possibility that although SRBC antigen is required in the cultures helper activity with low numbers of normal allogeneic T cells may not depend on T cells having specificity for this antigen.