Con A-propagated, auto-reactive T cell clones that secrete factors promoting high IgA responses

Four BALB/c T cell clones from among a set propagated in the presence of concanavalin A (Con A) were selected on the basis of their ability to produce supernatant factors promoting high IgA plaque-forming cell (PFC) responses by 2,4,6-trinitrophenyl-conjugated keyhole limpet hemocyanin (TNP-KLH)-primed splenic B cells in the presence of TNP-SRBC. Such clones could be derived from cultures containing T cells not only from gut-associated lymphoid tissue, but also from the spleen. The selected clones all proliferated well in the presence of syngeneic, irradiated APC without either Con A or exogenous IL-2, but required both APC and Con A to produce helper factors. Factors from three of the clones helped B cells both to proliferate and to differentiate into IgM, IgG and IgA PFC. Factors from the fourth clone helped B cells differentiate into IgA and IgG PFC and may have promoted switching to these isotypes but did not support either B cell proliferation or generation of IgM PFC. Cross-linking of B cell receptors for antigen was not required for the response to the helper factors since TNP-SRBC were unnecessary and high concentrations of them were actually inhibitory.