RAT LYMPHOID-CELL - DERIVED HISTAMINE AND 5-HYDROXYTRYPTAMINE RELEASING-FACTOR

The in vitro production of histamine releasing factor (HRF) by lymphoid cells of rats, both normal and infected with Nippostrongylus brasiliensis, has been studied. Spleen cells and thymocytes were cultured either alone or in the presence of mitogen (PHA, 10 and 50 mug/ml) and the dialysed cell-free supernatants were tested for histamine releasing activity on rat peritoneal and pleural mast cell in vitro. We found that spleen cells and thymocytes of normal rats stimulated with PHA in 24 h cultures generated a factor which released histamine and 5-hydroxytryptamine from mast cells, and this ability was potentiated following N. brasiliensis infection of rats - lymphoid cells donors. Pleural mast cells were more sensitive to the action of HRF than peritoneal cells. Rat HRF had an apparent m.w. of 50,000 to 70,000 daltons as determined by gel chromatography and was a heat stable protein inducing histamine release from homologous mast cells in a very rapid (complete in 1 - 2 min at 37-degrees-C), dose and temperature dependent secretory process.