Dependency of antibody titer on provirus load in human T lymphotropic virus type I carriers: an interpretation for the minor population of seronegative carriers.

To evaluate the prevalence of seronegative carriers of human T lymphotropic virus type I (HTLV-I), buffy coat samples from 1015 Okinawan high school students were tested by immunoassays and nested polymerase chain reaction (PCR). Among 17 HTLV-I carriers, 1 person who was seronegative and 1 who was PCR-negative were identified. gag and tax/rex PCR titers correlated with each other (r = .92; P < .001). Of the 17 carriers, 14 (82%) had high virus loads (geometric averages, 522 gag and 703 tax/rex copies/micrograms of DNA; 95% confidence intervals, 38-7260 and 75-6594, respectively). Carriers with low virus loads had < or = 2.2 gag copies. In the high-virus-load group, the gag PCR titers correlated with the antibody titers (r = 0.88; P < .001). The regression line intersected the minimum antibody detection level at 35 gag copies/micrograms of DNA. These results suggest that a small percentage of carriers may be seronegative.