994 NEUTRALIZATION OF HERPES SIMPLEX VIRUS BY ANTIBODY IN AMNIOTIC FLUID

The incidence of natally acquired Herpes simplex infections (HSI) has been estimated to be 1/7500 births, despite the fact that rates of asymptomatic shedding by pregnant women have been shown to be as high as 1/154. To investigate mechanisms which may explain the lower than expected incidence of clinical infection, amniotic fluid (AF) obtained during gestation and amniotic fluid and secretions (AF-S) obtained from the infants' mouths at delivery were tested for ability to neutralize HS. AF or AF-S were incubated with an equal volume of virus inoculum for 1 hr at 37°C. Neutralization of virus was assessed by reduction in expected plaque forming units (pfu). Maternal serum antibody was considered absent if the neutralization titer was <1:5, low if 1:5-1:39, and high if ≥1:40. AF and AF-S from 22 women whose serum titers were <1:5 did not neutralize HS. Ninety-six percent of AF or AF-S from 32 women with high serum antibody neutralized 50 pfu/0.lcc and 83% neutralized 500 pfu/0.1cc. Among women with low serum antibody, 52% of samples neutralized 50 pfu/0.1cc and 31% neutralized 500 pfu/0.1cc. Treatment with protein A to remove IgG also removed the neutralizing activity. Antibody to HS is, therefore, present in AF and the quantity present correlates with the mother's serum antibody titer. These results are consistent with a decreased risk of infection in infants of mothers with high antibody titers.