B cell activating factor(s) (BCAF) containing supernatant can induce all classes of immunoglobulin and IgG switches in resting B cells.

We have previously shown (L. Leclercq et al., Proc. Nat. Acad. Sci. 1984, 81:6491) that the supernatants of activated T helper cells can stimulate resting B cells to proliferate and to express early activation markers. The corresponding activity has been called B Cell Activating Factor or BCAF. Here we show that BCAF-containing supernatants can induce resting B cells to produce immunoglobulins of all isotypes as measured by enzyme linked immunoabsorbent assay. The isotype pattern obtained is similar to the one obtained when TH cells are cocultured with unprimed resting B cells. Furthermore, BCAF-containing supernatants induce IgG switches as measured by the secretion of IgG3, IgG1, IgG2a and IgG2b immunoglobulin by cell sorted surface IgG- resting B cells. These investigations confirm that BCAF-containing supernatants can act on resting B cells.