Feedback suppression of B cell colony formation by supernatants of B colony cells: Role of immunoglobulin

Summary We have reported previously that CD5 + B cells from mature B cell colonies provide a negative feedback signal to the growth of autologous B cell colonies. Now we have observed that supernatants from mature B cell colonies also provide a negative feedback signal to the growth of autologous B cell colonies. We investigated the mechanism of this effect by growing B cell colonies physically separated by a 0.45 μm filter from T cells in millicell‐CM chambers. Addition of colony supernatants to the T cell compartment reduced the number of B cell colonies by 28±6%. Colony numbers were reduced by 11±2 and 17±5% when the supernatants were added to the B cell or to both compartments, respectively. Pulsing T cells with the B cell colony supernatants before adding them to the colonies also decreased colony numbers by 33 ± 13%. The addition of exogenous Ig classes and IgG subclasses to B cells decreased B cell colony numbers, although the effect was variable. In the presence of T cells, IgG had the greatest suppressive activity and the subclass IgG4 was most suppressive. In the absence of T cells, high concentrations of IgG almost abolished B cell colony formation. We conclude that these supernatants provide a negative feedback signal either directly to B cells, or via T cells which may be mediated at least in part by Ig.