Histamine-releasing activity of lymphocyte supernatants of guinea pig spleen cell cultures.

We demonstrated the production of a histamine releasing factor (HRF) by 24-h cultures of guinea pig spleen cells which were stimulated or not with specific antigen (ovalbumin, OA) or mitogen (phytohemagglutinins or concanavalin A). HRF induced the release of histamine from homologous mesenteric mast cells in a dose-dependent fashion. The HRF-induced histamine release was not high compared to the release induced by calcium ionophore A23187, but higher than that induced by compound 48/80, polymyxin B and con canavalin A. The mast cells from sensitized guinea pigs released histamine when challenged with OA. We found that HRF-induced histamine release was additive to that induced by antigen, when both agents were added simultaneously to sensitized mast cells. The phenomenon was most significant when a suboptimal dose of antigen was used. Moreover, we did not observe any differences in the magnitude of HRF-induced histamine release between the mast cells from nonsensitized and sensitized guinea pigs. The time course of histamine release induced by HRF was significantly slower than that with specific antigen (10 min and 45 sec, respectively). Our results may suggest that HRF acts on mast cells through a different not immunological mechanism.