In cases where the end point titer (EPT) was outside the range of these dilutions, additional 2-fold dilutions were made either starting with a minimum dilution of 1 1:1000 or diluting to maximum of 1 1:2048000. to breastfeeding; the remainder occur or during delivery.1 The role of neutralizing antibodies (Nabs) in the setting of mother-to-child transmission (MTCT) has been extensively studied to determine if HIV-specific antibodies present at the time of exposure can protect against HIV infection. Several early studies, each relatively small, showed that non-transmitting mothers (NTM) tended to have more frequently detected and/or higher Nab responses than transmitting mothers (TM), suggesting a role for Nabs in reducing MTCT.2-4 However, additional studies reported discordant results regarding whether Nabs are important during all stages of MTCT, if at all.2,5,6 The association between Nabs and protection has also been somewhat dependent on the computer virus tested.5 No association was observed between infant infection risk and the breadth and potency of passively acquired antibodies in infants exposed to HIV-1 during breastfeeding.7 It is unclear if the results from this study in infants indicate there is simply poor vertical transfer of HIV-1-specific Nabs or that this breadth and potency of maternal Nabs are not a factor in protection against breastmilk HIV-1 transmission. Placentally acquired antibodies reach their highest level in the infant during the third trimester. Studies in nonhuman primates have exhibited passive transfer of HIV-1 specific Nabs8,9, but little is known about the transfer of maternal HIV-1-specific Nabs in humans. One study of 35 mother/infants pairs that assessed Nabs against two lab-adapted HIV-1 strains showed a strong correlation between maternal and infants Nabs.10 However, responses to more relevant circulating variants of HIV-1 were not examined. Another study that explored the relationship between maternal and infant antibodies showed variance in antibody transfer based on antigen specificities and IgG subclasses, indicating transfer may vary by antibody type.11 Thus, these studies suggest that mother-to-child transfer of HIV-1-specific Nabs may be affected by the nature of the Nabs, including antibody specificity. To address this hypothesis, we measured the levels of HIV-specific antibodies including Nabs, against three circulating HIV-1 variants that symbolize the dominant HIV-1 subtypes in the population under study to determine if the levels in the infant were similar Uridine triphosphate to the mother, suggesting efficient transfer. Materials and methods Samples Plasmas tested in the current study were from mother/baby pairs who participated in the breastfeeding arm of a randomized clinical trial carried out in Nairobi, Kenya.1 Plasmas from your mothers were obtained around the time of delivery and the infant plasmas were obtained within the first week after birth, a time when passively transferred antibody levels should be high. Both women and infants were antiretroviral therapy na?ve and mother/infant pairs were included in this study based on these criteria: 1) the mother breastfed, 2) the mother had a plasma sample available around delivery, 3) the infant was HIV DNA PCR negative at birth, 4) the infant was either detected as HIV positive after birth or was followed for at least 3 months if HIV negative, and 5) the infant had a plasma sample within the first week after birth.7 Sixty mother/infant pairs met these criteria and were included in the study. The ethical evaluate committees of the University or college of Nairobi, University or college of Washington and Fred Hutchinson Malignancy Research Center approved this study and all subjects provided written consent. Uridine triphosphate Detection of HIV-1 Envelope-specific IgG HIV-1 Envelope-specific IgG titers were estimated using an enzyme-linked immunosorbent assay (ELISA) performed as previously layed out using a HIV subtype A gp120 protein (BL035; Immune Technology Corp., New York, NY).12 Plasmas were diluted starting at 1:4000 followed by 2-fold serial dilutions up to a maximum dilution of 1 1:512000. In cases where the end point titer (EPT) was outside the range of these dilutions, Uridine triphosphate additional 2-fold dilutions were made either starting with a minimum dilution of 1 1:1000 or diluting to maximum of 1 1:2048000. The EPT was defined as the reciprocal plasma dilution at which the average optical density (OD) value was greater than or equal to twice the average OD value of the background. For the purposes of analyses, in cases in which the EPT was less than the lowest dilution tested, the midpoint value (500) between the least expensive dilution and zero was assigned. The EPT results represent the average of two impartial duplicate assays. Viruses & Neutralization Assay Three HIV-1 envelopes representing two subtype Rabbit polyclonal to AnnexinA1 A (Q461.d1 & Q842.d16) and one subtype D (QD435.A4) variants, were used to generate pseudoviruses as described.7 These envelopes were initially cloned from 3 viruses isolated early in infection, directly from blood of 3 Kenyan women. Neutralization assays were performed by infecting TZM-bl cells with the.