Gamma interferon induction in human thymocytes activated by lectins and B cell lines.

Human thymocytes in culture synthesized small quantities of interferon (IFN) when stimulated by the lectins concanavalin A or phytohemagglutinin. IFN production by lectin-activated thymocytes was enhanced in the presence of live B lymphoblastoid cells, irradiated B lymphoblastoid cells, or the conditioned medium from B lymphoblastoid cell cultures. The IFN synthesized in mixed cultures had characteristics of IFN-gamma, whereas the IFN synthesized by B lymphoblastoid cells alone could be identified as IFN-alpha on the basis of its neutralization with specific antisera and stability at pH 2. These findings indicate that human thymocytes in culture synthesize IFN-gamma and that B lymphoblastoid cells and their products considerably stimulate IFN-gamma synthesis by lectin-activated human thymocytes in culture. This stimulation was not diminished in the presence of antibodies to IFN-alpha, indicating that IFN-alpha production by B lymphoblastoid cells was not responsible for the stimulatory effect. Removal of adherent cells from thymocyte suspensions did not abrogate IFN-gamma production.