Tetrapeptides of the eosinophil chemotactic factor of anaphylaxis (ECF-A) enhance eosinophil Fc receptor.

Certain mast cell products, including the tetrapeptides Ala-Gly-Ser-Glu (Ala4) and Val-Gly-Ser-Glu (Val4) of the eosinophil chemotactic factor of anaphylaxis (ECF-A) and histamine, are preferentially chemotactic for eosinophils in vitro. Amino acid substitutions or modifications of the ECF-A tetrapeptides may substantially alter the chemotactic activity of human eosinophils. The cellular mechanism whereby ECF-A tetrapeptides enhance IgG-dependent killing of schistosomula by rat eosinophils is, however, unclear. We now report that the parent tetrapeptides and the substituted analogue Val-Pro-Ser-Glu (Pro3), but not histamine, increase the number of rat and human eosinophils that form rosettes with erythrocytes bearing IgG antibodies. Moreover, we find a correlation between the effect of these substances on the expression of rat eosinophil IgG Fc receptors and their capacity to increase the IgG-dependent cytotoxicity of rat eosinophils for Schistosoma mansoni schistosomula.