Pharmacological control of human basophil histamine release stimulated by eosinophil granule major basic protein.

Eosinophil granule major basic protein (MBP) is a 13,800 MW arginine-rich polypeptide that is unique among basic molecules in its ability to stimulate human basophil histamine release. We examined the Ca2+ requirements and pharmacological regulation of MBP-stimulated histamine release. Minimal MBP-induced histamine release occurred in the absence of extracellular Ca2+, whereas addition of 0.1 mM Ca2+ resulted in 70% of the maximum histamine release response. Maximum histamine release required 0.5 to 1 mM extracellular Ca2+. The MBP-induced histamine release was blocked by a calmodulin antagonist and by theophylline and was partially inhibited by an inhibitor of phospholipase A2. Release was unaffected by inhibition of protein kinase C. Basophil pretreatment with pertussis toxin also resulted in a concentration-dependent inhibition of release, suggesting involvement of a GTP regulatory protein in the activation mechanism. Histamine release stimulated by a 13,900 MW poly-L-arginine exhibited a dissimilar pharmacological profile from that of MBP. These results support the non-cytolytic nature of the MBP activation mechanism and identify pharmacological approaches for control of MBP-induced mediator release.

Donor sensitivity to basophil activation by eosinophil granule major basic protein.

Leukocytes of 22 individuals were incubated with a suboptimal concentration of eosinophil granule major basic protein and the amount of histamine release was determined. Cells from 20 of the 22 donors had a histamine release of greater than or equal to 15%. The use of selected donors on repeated occasions revealed significant variability in individual donor responsiveness. The findings support a role for major basic protein activation of human basophils in allergic reactions.

Stimulation of basophil and rat mast cell histamine release by eosinophil granule-derived cationic proteins.

Major basic protein (MBP), an arginine-rich basic polypeptide that constitutes the crystalloid core of the large specific eosinophil granule, has previously been shown to stimulate noncytolytic histamine release from human basophils and rat mast cells by an IgE-independent mechanism. Two additional basic polypeptides present in eosinophil granules, eosinophil cationic protein (ECP) and eosinophil-derived neurotoxin (EDN), were examined for similar activity in the present study. Acid-solubilized eosinophil granules were fractionated by chromatography on a Sephadex G-50 column. Incubation of basophil-containing human mononuclear cells with the individual column fractions demonstrated that histamine release occurred only with the fractions that contained MBP. The selectivity of the basophil response for MBP was confirmed by using equimolar concentrations of purified MBP, ECP, and EDN. In contrast, both MBP and ECP, but not EDN, stimulated histamine release from purified rat peritoneal mast cells. Reduction and alkylation of the MBP molecule diminished the response of human basophils to MBP but enhanced the potency of the molecule with rat mast cells. The distinct potency of MBP as a stimulus for histamine secretion from human basophils suggests that eosinophil release of MBP may be a specific event in the augmentation of immediate hypersensitivity reactions and other disorders characterized by eosinophilia.