Characterization of polymorphonuclear leukocyte aggregation in vitro induced by heat-inactivated group B streptococcus.

We studied the aggregatory characteristics of human polymorphonuclear leukocytes (PMNs) in response to heat-inactivated group B streptococcus. PMNs suspended in physiologic salt solution do not aggregate to heat-inactivated group B streptococcus (GBS) unless the GBS is previously opsonized in autologous plasma. The aggregating activity of both opsonized GBS and activated plasma are reduced if the plasma is decomplemented before incubation with GBS. Pretreatment of PMNs with pronase inhibited opsonized GBS-induced aggregation, suggesting aggregation via cell membrane receptors for opsonic fragments of C3. Pronase pretreatment had no significant effect on aggregation induced by activated plasma or arachidonic acid. Unlike PMNs in physiologic salt solution, PMNs suspended in plasma aggregate when stimulated by unopsonized GBS. GBS aggregates PMNs via complement cascade activation, opsonization, and interaction with cell membrane receptors to stimulate cellular mechanisms resulting in PMN aggregation.