Humoral Responses to the Immunodominant gag and env Epitopes of Human T-Lymphotropic Virus Type I among Melanesians

The immune responsiveness to the immunodominant B-cell epitopes of human T-lymphotropic virus type I (HTLV-I), derived from the external envelope glycoprotein (recombinant MTA-1^162–209, synthetic Env-1^119–214, and Env-5^242–257) and the gag-encoded matrix protein (Gag-1a^102–117), was analyzed in 19 HTLV-I-seropositive and 51 HTLV I-seroindeterminate Melanesians from Papua New Guinea and the Solomon Islands. The reactivities of seropositive Melanesian specimens to MTA-1 (100%), Env-5 (89%), and Gag-1a (79%) were similar to that seen with U.S. specimens, while reactivity to Env-1 was lower in Melanesian specimens (68%). Minimal reactivity was found to the env epitopes among the 51 HTLV-I-seroindeterminate Melanesians, but 29 (57%) reacted to Gag-1a. The failure to detect HTLV-I gag, pol, env, and tax gene sequences by polymerase chain reaction among the seroindeterminate Melanesians suggests that such reactivities to the Gag-1a epitope represent cross-reacting antibodies with closely related microbial or cellular proteins.