Flow cytometric study of the expression of neutral endopeptidase (CD10/CALLA) on the surface of newborn granulocytes.

The susceptibility of newborn infants to bacterial infections is well documented. Neutrophils play an important role in defense against bacterial infection, the most common kind of infection in the newborn period. Many studies of lymphocyte surface characteristics during that period of life are available, but there are no reports on the surface immunophenotype of the granulocytes at birth. Because some of their membrane associated antigens have been identified as enzymes (CALLA/CD10), neutral endopeptidase, and (CD13) amino peptidase that could play a role in the biological functions of neutrophils, a study of the membrane phenotype appeared potentially important. Using flow cytometry, we studied the expression of a panel of the antigens expressed on mature neutrophils including CD10, CD13, and CD33 in 28 full-term babies and 19 adults. A significantly (p < 0.001) lower expression of CD10, CD13, and CD33 was found in full-term babies compared with 19 adults. These data raise two points: first, that because CD10 is detected only on segmented granulocytes, the low level of CD10 observed in neonates is consistent with a degree of immaturity of the neutrophil membrane, and second, that the deficiency of endopeptidase may impair neutrophil interactions with peptide effectors and thus play a role in the increased susceptibility to bacterial infections exhibited in newborns.