The numbers of eosinophils recruited locally to abraded human skin were measured in eight atopic and eight non-atopic volunteers, at time intervals over 24 hr, following the application of an ECF-A tetrapeptide (Val-Gly-Ser-Glu) or histamine. In all subjects the higher doses of the peptide (10-4 and 10-6 mol/1) or histamine (10-3 and 10-5 mol/1) produced significantly greater counts than the Tyrode's diluent alone. The counts produced with the lowest dose of peptide (10-8 mol/1) or histamine (10-7 mol/1) were not significantly different from the control. The peptide or histamine evoked a greater local eosinophilia in the atopics than the non-atopics. This effect was probably independent of the peripheral blood eosinophil counts since at the time of study the numbers of circulating eosinophils between the two groups were not significantly different. In the atopics, histamine in doses of 10-3 and 10-5 mol/1 were required to give the same eosinophil response as that obtained with 10-4 and 10-6 mol/1 of the peptide, respectively.
It is suggested that the relative paucity of eosinophils recruited by locally applied ECF-A peptide or histamine, when compared to antigen-induced eosinophilia, is due either to an inability to mimic the events associated with the release of these mediators from mast-cells or the involvement of other pharmacological agents.