Antigen‐specific major histocompatibility complex‐restricted helper T cell clones are sufficient to induce unprimed B cells to switch and to secrete IgG and IgA in a primary in vitro polyclonal response

Abstract

To investigate the role of helper T (T_h) cells in the regulation of the production of the various immunoglobulin (Ig) classes and subclasses, we have used poly (Glu⁶⁰Ala³⁰Tyr¹⁰) (GAT)‐specific, major histocompatibility‐complex‐restricted T_hcell clones to stimulate unprimed B cells. The T cells used in these studies were Thy‐1⁺, Lyt‐l⁺, Lyt‐2⁻ and lacked Fc receptor for IgM, IgG and IgA, and the unprimed splenic B cells were selected by the fluorescence‐activated cell sorter for their lack of expression of surface (s)IgG and by panning for their lack of expression of sIgA. We have taken advantage of the ability of some antigen‐specific major histocompatibility complex (MHC)‐restricted T_h cell clones to polyclonally activate unprimed B cells in vitro in the presence of high doses of antigen. We have shown that under these conditions, an antigen‐specific MHC‐restricted T_h cell clone is sufficient to induce the switch of sIgG⁻ sIgA⁻ unprimed B cells to IgG and IgA, as well as the expansion of these cells and their differentiation into IgG and IgA‐secreting cells. Isotype‐specific T_h cells thus do not seem to be an absolute requirement for the production of the various IgG subclasses and of IgA.