Association between maternal antibodies to the external envelope glycoprotein and vertical transmission of human T-lymphotropic virus type I. Maternal anti-env antibodies correlate with protection in non-breast-fed children.

Vertical transmission of human T-lymphotropic virus type I (HTLV-I) depends primarily on breast-feeding; substitution of bottle-feeding has reduced the transmission rate from 20% in breast-fed children to 3% among bottle-fed. To determine the correlates of transmission for long breast-feeding (> or = 6 mo), short breast-feeding (< 6 mo), and bottle-feeding mothers, the antibody titers of transmitter (T) mothers and non-transmitter (nT) mothers were analyzed by using synthetic and recombinant epitopes representing the immunodominant epitopes of gag (Gag1a, r24), env (Env1/5, MTA1, RE3), and tax (Tax8/22-24) proteins. Seroreactivity to gag and tax epitopes was not significantly different except for anti-r24 antibody titer, which was significantly higher among T-mothers (geometric mean 134) when compared with nT-mothers (62) in the long-feeding group (P < 0.001). Profiles of antibody titers against env epitopes were different. Within the long-feeding group, Env1/5, MTA1, and RE3 titers were significantly higher among T-mothers (258, 1,476, and 738, respectively) when compared with nT-mothers (106, 279, and 320, respectively) (P < 0.01 for all three epitopes). In contrast, within the bottle-feeding group, antibody titers to Env1/5 (269) and RE3 (418) among nT-mothers were significantly higher than those among T-mothers (80 and 113, respectively) (P < 0.01). These data confirm that high-titered anti-HTLV-I antibodies in the long-feeding group correlate with milk-borne transmission of HTLV-I and, more importantly, imply that maternal anti-env antibodies may reduce the risk of non-milkborne infection.