Role of complement receptors in opsonophagocytosis of group B streptococci by adult and neonatal neutrophils.

The role of complement receptors in bactericidal activity for types III and Ia group B streptococci (GBS) by adult or neonatal polymorphonuclear leukocytes (PMNL) was explored using polyclonal and monoclonal antibodies to complement receptors one (CR1) and three (CR3). In an opsonophagocytic assay, selective blockade of the CR3 sugar or lectin-like binding site on adult or neonatal PMNL effected a significant reduction in killing of both GBS serotypes that was more pronounced for type III. In contrast, blockade of the iC3b binding site effected greater inhibition of bactericidal activity for type Ia than for type III GBS. When both the CR3 sugar or lectin-like binding site and CR1 were blocked, inhibition was enhanced for type Ia GBS by adult PMNL and for both serotypes by neonatal PMNL. These results demonstrate a role for both CR1 and CR3 in the opsonophagocytosis of GBS. Possibly, differences in CR3 epitope utilization contribute to the differential virulence among GBS serotypes in neonates.