Neutralization of herpes simplex virus by antibody in amniotic fluid

The ability of amniotic fluid to neutralize herpes simplex virus type 2 (HSV-2) was quantitated and compared with the serum neutralization titer in 158 pregnant women. Neutralizing activity was expressed as the ability of 0.1 ml of amniotic fluid to reduce the expected number of plaque-forming units (pfu) in the inoculum by 99%. All amniotic fluid samples from 32 women with serum titers of 1:40 or greater neutralized 5 pfu or more; at term, 96% of these fluid samples neutralized 50 pfu or more, 83% neutralized 500 pfu or more, and 61% neutralized 5000 pfu or more. Only 76% of the amniotic fluid samples obtained at term from women with serum titers of 1:5 to 1:39 contained detectable neutralizing activity and only 8% neutralized 5000 pfu or more. None of the amniotic fluid samples from 30 women with serum titers less than 1:5 neutralized 5 pfu or more. All neutralizing activity was removed when immunoglobulin G was removed from the amniotic fluid samples. Sera were obtained from 51 pregnant women 4 to 8 weeks prior to delivery. All women with serum titers of 1:40 or higher gave birth to infants who also had serum titers of 1:40 or higher. Therefore, it is possible to predict the neutralization titer in amniotic fluid and in the infant's serum by measuring the mother's titer in the third trimester.