Impaired Opsonic Activity but Normal Phagocytosis in Low-Birth-Weight Infants

Abstract

Blood of 19 term and 19 low-birth-weight (LBW) neonates was studied for polymorphonuclear phagocytosis, intracellular killing and serum opsonin activity. Serums from 12 of 13 infants under 1925 gm had inadequate opsonins against Staphylococcus aureus 502A and Serratia marcescens when combined with either autologous or normal adult leukocytes. Serums from adults, term newborn infants and physiologically hypogammaglobulinemic infants did not exhibit this serum abnormality. With adult opsonin, cells from all 15 normal term and 13 of 14 normal LBW neonates phagocytized and killed bacteria normally. However, cells from six of nine term and LBW infants with abnormal clinical findings showed diminished phagocytic and killing rates. Levels of γG and β1c globulins were significantly higher in term than in LBW serums; γM and γA globulins were similar in the two groups. Low levels of γG globulin in LBW infants are probably the major factor responsible for their opsonic defect.