Eosinophils and neutrophils of human neonates have similar impairments of quantitative up-regulation of Mac-1 (CD11b/CD18) expression in vitro.

Neonatal neutrophils have Mac-1-related functional abnormalities that may contribute to the enhanced susceptibility of neonates to bacterial infections. We developed a flow cytometric method using differences in light scattering and CD16 expression to distinguish eosinophils from neutrophils and studied their responses to stimulation in vitro. Mean forward light scatter was 20-60% greater for adult neutrophils than eosinophils, p less than or equal to 0.001, and side scatter was 30-60% greater for eosinophils than neutrophils, p less than or equal to 0.01, both before and after stimulation. Light scatter of neonatal and adult eosinophils did not differ. Mac-1 expression on adult eosinophils increased 60% after warming without specific stimulation and further increased 5-fold after incubation with 1 microM A23187, p less than 0.0001. Platelet activating factor and recombinant C5a produced modest increases in eosinophil Mac-1 expression, while N-formyl-met-leu-phe and leukotriene B4 had minimal effects. Histamine and the eosinophil chemotactic factor of anaphylaxis tetrapeptides had no effect on either Mac-1 or CR1 (CD35) expression. After stimulation with 1 microM A23187, eosinophils from eight healthy neonates at term expressed less Mac-1 than eosinophils from eight adults (mean +/- SD: 60.0 +/- 17.2 versus 89.1 +/- 12.8, p = 0.001) by the same ratio as neonatal to adult neutrophils (121.5 +/- 17.9 versus 178.2 +/- 11.7, p = 0.0004). We conclude that neonatal eosinophils and neutrophils have similar impairments of quantitative Mac-1 up-regulation. Further studies are needed to determine if neonatal eosinophils also have functional abnormalities related to Mac-1.