Opsonic activity in cord blood: comparison between normal and elevated immunoglobulin M infants.

In order to clarify the relation between opsonic activity (OA) in newborn infants and their gestational age, we determined OA by Cypiridina luciferin analog-dependent chemiluminescence (MCLA-CL). In addition, complement C3 which plays the major role in OA, was determined by the two-dimensional immunodiffusion method. Although OA and C3 in newborn infants increased in proportion to their gestational age, the levels were significantly lower in full-term infants than in adults. In neonates with IgM levels of more than 30 mg/dL at birth, both OA and C3 levels were significantly higher than in normal neonates, yet these levels were significantly lower than in adults. These findings suggest that low opsonin activity is an important factor in neonatal susceptibility to infection. When OA is measured by chemiluminescence, MCLA-CL is the preferred technique to luminol-dependent chemiluminescence.