Cholera toxin-sensitive and insensitive signaling via surface Ig

We have observed that a 2-h pretreatment of murine B cells with cholera toxin (CT) renders the B cell incapable of receiving an activation signal via surface Ig as measured by cell volume increase and entry into the S phase of the cell cycle. In contrast, CT pretreatment does not inhibit the delivery of a signal by IL-4, as measured by increase in cell volume. In fact, CT pretreated B cells are able to respond to anti-Ig in the presence of IL-4, as measured by both an increase in cell size and entry into S suggesting that IL-4 overcomes the effects of CT on normal B cell activation. Despite blocking the anti-Ig-mediated entry into the cell cycle, CT was not able to interfere with the induction of nonresponsiveness by anti-Ig in normal B cells or with the delivery of growth-inhibitory signal to the B cell lymphoma WEHI-231. These results suggest that there are two signaling pathways mediated by cross-linking of surface Ig: one pathway sensitive and the other insensitive to modulation by CT.