1145 A GROUP B STREPTOCOCCAL (GBS) EXTRACT INDUCES NEUTROPHIL AGGREGATION AND NEUTROPENIA

Neutropenia has been commonly associated with neonatal GBS infections. The cause of the neutropenia, however, is poorly understood. The intravenous infusion of a trichloroacetic acid extract of GBS (GBS-TCA) into 1-6 day old lambs (dose 1 mg/kg), induced a rapid decrease in peripheral blood PMNs (0 time-3.1 × 103/mm3 ± 0.5 vs 2.2 × 103/mm3 ± 0.7, 5 min after infusion; p < 0.01, n=6). Neutropenia persisted throughout the 20 min post infusion period. Pulmonary histology demonstrated extensive accumulations of PMNs in the interstitial space after GBS-TCA administration. To determine if GBS-TCA could induce aggregation in vitro, PMNs were isolated from adult and cord blood specimens. Aggregation was measured using a Sienco aggregometer. The maximal change in light transmission (ΔT) over 1 min was obtained from aggregation curves. Serum alone did not aggregate PMNs. However, GBS-TCA incubated in serum (1 hr) induced prompt PMN aggregation. A typical dose response occurred and was maximal at 10 mg/ml (GBS-TCA in serum-mean ΔT 12.3% ± 2.8 vs GBS-TCA in PBS-mean ΔT 2.5% ± 2.1; p < 0.001, n=8). These data demonstrate that cell free GBS products may induce PMN aggregation in serum. PMN aggregates may be nonspecifically removed from the peripheral circulation by entrapment in the pulmonary vasculature. GBS induced PMN aggregation may play an important role in the neutropenia and pulmonary manifestations commonly associated with neonatal GBS infections.