Soluble anti-mu monoclonal antibodies prime resting B cells to secrete immunoglobulins in response to interleukins-4 and -5.

Soluble anti-immunoglobulin (Ig) antibodies have been generally found to inhibit Ig secretion in B cells, via largely unknown mechanisms. To investigate this phenomenon further a two-step culture system was used in which B cells are primed for 24-72 h with various soluble monoclonal or polyclonal anti-Ig antibodies: after washing the cells were placed in readout cultures with a combination of interleukin (IL)-5 and IL-4. Using this protocol B cells primed with (mitogenic or nonmitogenic) anti-mu monoclonal antibodies differentiated into large numbers of IgM-secreting cells, comparable to responses to lipopolysaccharide. In contrast, priming with polyclonal rabbit anti-Ig or monoclonal anti-kappa antibodies, markedly inhibited Ig secretion induced by IL-4 + IL-5. In addition, anti-mu was markedly inhibitory if left in the readout cultures with the two lymphokines. These results, therefore, indicate that appropriate cross-linking of surface IgM receptors on B cells can prime the cells to secrete Ig when they are restimulated by T cell-derived lymphokines in the absence of anti-mu. In contrast co-ligation of both surface IgM and surface IgD receptors apparently results in powerful inhibition of Ig secretion, which is not reversed by stimulation with IL-4 plus IL-5.