Postnatal maturation of total cell content and up-regulated surface expression of Mac-1 (CD11b/CD18) in polymorphonuclear leukocytes of human infants.

Markedly deficient expression of membrane-activated complex 1 (Mac-1; CD11b/CD18) by polymorphonuclear neutrophils (PMN) of human neonates compared with adults is well documented. To define postnatal maturation of Mac-1 expression of PMN, lysates of PMN from 21 infants, aged 1-14 months, and concurrent adult controls were assayed by ELISA for total cell content of Mac-1 and LFA-1 (CD11a/CD18), and LFA-1 content was within the normal adult range at all ages tested. Mac-1 content was approximately 50% of adult levels for infants 1-2 months of age and steadily increased to reach normal adult levels by 11-12 months of age. For a separate group of 25 infants, aged 0.5-11 months, measurement of surface expression of Mac-1 and LFA-1 on activated PMN by immunofluorescence flow cytometry yielded results that were similar to those obtained by ELISA.