MONOCYTE CHEMOTACTIC AND ACTIVATING FACTOR IS A POTENT HISTAMINE-RELEASING FACTOR FOR BASOPHILS

Monocyte chemotactic and activating factor (MCAF) is a recently cloned cytokine that causes chemotaxis of basophils. In our pursuit of cytokines affecting basophil function, we studied the effect of MCAF on histamine secretion from basophils. Leukocytes from 20 donors, 10 allergic and 10 normal subjects, were studied. MCAF caused dose-dependent release of histamine at concentrations of 10(-8) and 10(-7) M, and the mean release was 31.25 +/- 2.9% at the highest concentration. In the same experiments the mean histamine release by anti-IgE and histamine releasing factor (HRF) was 27.05 +/- 4% and 32.70 +/- 2.7%, respectively. All 20 subjects responded to MCAF with significant histamine release. Allergic subjects released significantly more histamine than normals in response to anti-IgE (P < 0.01) but not to MCAF (P = 0.2) and HRF (P = 0.1). The histamine release was significantly correlated between MCAF and HRF (P < 0.01), but not between MCAF and anti-IgE (P < 0.05). The histamine release by MCAF was complete within the first 3 min. MCAF-induced degranulation was a calcium-dependent process. Leukocytes depleted of monocytes responded equally well to MCAF. Using an anti-MCAF affinity column we determined that > 50% of HRF activity of crude PBMC supernatant could be attributed to MCAF. Thus, we established that MCAF is a potent secretagogue for basophils.