Clonal analysis of antigen-specific interactions between T cells and genetically engineered B cells.

In order to investigate T cell-B cell interactions we constructed monoclonal, antigen-specific T- and B-cell populations. The Ia+ B-cell lymphoma A20-2J was transfected with trinitrophenyl (TNP)-specific heavy (mu) and light (kappa) chain Ig genes. A hapten-carrier complex (TNP-keyhole limpet hemocyanin (KLH)) bound to the surface Ig expressed on the transfectant and was presented to carrier-specific T-cell hybridoma clones at markedly low doses of antigen (0.01 microgram/ml) and in an Ia-restricted fashion. Two responses were elicited in the responding T-cell clones: (i) high levels of IL-2 secretion (320 units/ml), and (ii) cytotoxicity directed against the antigen-presenting B cell. This cytotoxicity was inhibited by D-mannose and was directed against innocent bystander cells, unlike cytotoxicity mediated by NK cells or alloreactive cytotoxic T lymphocyte. Helper and cytotoxic functions were often present in different T-cell hybridomas but some clones exhibited both activities. One representative T-cell hybridoma exhibited strong helper function for TNP-primed splenic B cells as detected in a plaque-forming cell assay, but was cytotoxic toward antigen-presenting B cells. Such monoclonal assay systems for studying cognate interactions of heterogeneous T cells and specific antigen-presenting cells will provide us with valuable new approaches for the study of antigen-specific T-cell regulation of B-cell activation in immune responses.