Con A induction of IgG secretion from a B-lymphoid tumour cell line, A20.

We have examined the effect of concanavalin A (Con A), a conventionally known T-cell mitogen, on the induction of Ig secretion from BALB/c B lymphoid cell lines expressing membrane IgM (X16C8.5, BALENTL 17.7.2 and BCL1) or membrane IgG (A20 and M12.4). A20 tumour cells, but not other tumour cells, responded to Con A by secreting Ig as measured by the reverse plaque-forming cell (PFC) assay. Another typical T-cell mitogen, phytohaemagglutinin (PHA), did not have any effect on the differentiation of A20 tumour cells. The addition of NaN3 abolished the PFC formation, showing that IgG PFC formation of A20 tumour cells was due to the active synthesis of secreted IgG and not due to the shedding of mIgG. The increase in the biosynthesis of secreted IgG from A20 tumour cells by Con A was also observed by polyacrylamide gel electrophoresis. The ability of Con A to induce IgG secretion from A20 tumour cells was abolished by the addition of alpha-methylmannoside, confirming that Con A itself, and not some contaminating material in Con A, induced the maturation of A20 tumour cells. Con A was also shown to induce Ig secretion, but not proliferation, in a subset of normal B cells. Thus, we conclude that Con A does give a differentiation signal to a subset of B cells.