J A Grant

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 less than 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 less than 0.01), but not between MCAF and anti-IgE (P greater than 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 greater than 50% of HRF activity of crude PBMC supernatant could be attributed to MCAF. Thus, we established that MCAF is a potent secretagogue for basophils.

Histamine-Releasing Factors and Inhibitory Factors

Peripheral-blood mononuclear cells (MNC) synthesize several histamine-releasing factors (HRF) spontaneously and when stimulated. Some of the characterized cytokines have histamine-releasing activity, especially connective tissue activating peptide III, neutrophil-activating peptide 2 and interleukin-3 (IL-3). At least two species of HRF remain to be characterized. MNC also secrete a histamine release-inhibitory factor (HRIF), which is a highly specific inhibitor, because it antagonizes only HRF. IL-8 resembles the low-molecular-weight species of HRIF in terms of size and specificity.

Antigen-Induced Histamine Release from Guinea Pig Basophils

Guinea pig blood was found to contain an average of 106 +/- 21 ng/ml of histamine. Of this total, approximately 85-90% was of platelet origin and the rest from basophils. Basophils contain about 0.72 pg of histamine/cell. Concanavalin A (1-5 microgram/ml) induced the release of approximately 65% of the basophilic histamine. When basophils were isolated from animals sensitized to ovalbumin or keyhole limpet hemocyanin, addition of the appropriate antigen induced histamine release at concentrations of 0.01 microgram/ml or lower. Individual animals were studied over time by repetitive bleeding. The circulating basophils remained sensitized for at least 17 weeks postsensitization. However, release did not occur if animals had been sensitized less than 7 days earlier. This assay facilitates the investigation of basophil sensitization since animals can be studied on several occasions following immunization. The mechanisms, timing and role of basophil sensitization in various types of immune and hypersensitivity reactions can now be evaluated.