IgE-B cell-generating factor from lymph node cells of rats infected with Nippostrongylus brasiliensis. II. Effector mechanisms of IgE-B cell-generating factor

Cell-free culture supernatants (CFS) of mesenteric lymph node cells from Nippostrongylus brasiliensis-infected rats specifically increase the proportion of IgE-bearing cells in normal rat bone marrow cultures without changing the proportion of IgM-bearing cells and IgG2a-bearing cells. Virtually all of the IgE-bearing cells appearing in the culture carried IgM determinants on their surface. Precursors of IgE-bearing cells in normal bone marrow cells were removed by depletion of immunoglobulin-bearing cells. These findings indicate that IgE-B cell-generating factor converts IgM-bearing virgin B cells to IgM-IgE double bearing cells. Pretreatment of normal bone marrow cells with mitomycin C failed to inhibit the generation of IgE-bearing cells by the soluble factor. Indeed, most of IgE-bearing cells generated in cultures of mitomycin C-treated bone marrow cells did not contain ³H-thymidine, which was present during the entire culture period. It appears that DNA synthesis is not required for the differentiation of IgM-bearing cells to IgE-IgM double bearing cells. However, the appearance of IgE-bearing cells in cultures of normal bone marrow cells by CFS was abated by 0.5 μg/ml of actinomycin D or by pretreatment of the cells with pactamycin. These findings suggest that the observed differentiation involves some process dependent on transcription of DNA and protein synthesis.