Mediators from cloned T helper cell lines affect immunoglobulin expression by B cells.

When cloned T helper cells encounter antigen presented by I-A-compatible macrophages, soluble mediators are produced that affect the differentiation and activation of normal B lymphocytes and cell lines of the B lineage. Exposure to such T cell culture supernatants causes two effects in the murine 70Z/3 cell line, which represents a pre-B stage of differentiation. These cells begin to synthesize Ig light chains and gain membrane Ig that is detectable by immunofluorescence. Two other effects are seen after similar treatment of the WEHI-279.1 murine cell line, which represents a mature, Ig+ B cell. These cells shift the ratio of mu chains produced from mostly membrane to mostly secretory type and begin to secrete large amounts of IgM, which can be detected either by biosynthetic radiolabeling followed by immunoprecipitation or by a staphylococcal protein A plaque assay. The majority also die. Similar to WEHI-279.1, normal small resting B cells also show the shift from membrane mu to secretory mu and are activated to Ig secretion after exposure to these supernatants. These results show that products from T cell immune reactions exert multiple effects on B cell development and activation, at several stages of teh B cell developmental pathway. The observed change range from nuclear processes, including gene transcription and RNA splicing, to such post-translational aspects as protein processing, catabolism, membrane architecture, and cell survival.