Activation of guinea pig lymphocytes and mast cells by grain-dust extract

Previous studies have demonstrated that grain dust can stimulate lymphocyte proliferation and the production of interleukin-1 by macrophages. This study was undertaken to investigate whether grain dust could stimulate the production of histamine-releasing factor (HRF) by guinea pig spleen cells. We also studied the direct action of grain dust on guinea pig lung mast cells and basophils. Plastic nonadherent cells from immunized animals were cultured for 24 hours in the presence of grain dust or lipopolysaccharide, and the cell-free supernatants were assayed for HRF activity in the mast cell and basophil histamine release test. Lung mast cells were isolated by enzymatic digestion and discontinuous Percoll gradient centrifugation. It has been demonstrated that grain dust stimulated the production of HRF by spleen cells from the immunized animals but not from the control animals. Stimulation of spleen cells with lipopolysaccharide did not enhance the HRF production. Gel chromatography of grain dust-stimulated supernatant revealed that HRF has a molecular weight in the range of 50 to 70 kd and 5 to 8 kd. We also found that grain dust directly released significant amount of histamine from both mast cells and basophils. The results of this study suggest that grain dust contains some potent active substances that can activate lymphocytes, mast cells, and basophils.