To identify factors that may modify the heterosexual transmission of human T cell leukemia/lymphoma virus type I (HTLV-I), 534 married couples enrolled in the Miyazaki Cohort Study between November 1984 and April 1989 were studied: 95 husband HTLV-I-seropositive (H+)/wife seropositive (W+), 33 H+/W-, 64 H-/W+, and 342 H-/W-. After 5 years of follow-up, seven seroconversions occurred and clustered significantly among serodiscordant pairs (relative risk [RR] = 41.2); the rate of transmission was 3.9 times higher if the carrier spouse was male (P = .19). Among H+/W- couples, husband's age > or = 60 years strongly predicted seroconversion in the wives (RR = 11.5). All 4 carrier husbands whose wives seroconverted had HTLV-I titers > or = 1:1024 (P = .04) and were anti-tax antibody positive (P = .06). In cross-sectional analysis, total parity also was independently associated with wife's serostatus but only length of marriage with husband's. Overall, sexual transmission of HTLV-I was primarily from older infected husbands to their wives, with husbands' viral status being an important factor.

The purpose of the Miyazaki Cohort Study is to describe and analyze the natural history of human T-cell lymphotropic virus type I (HTLV-I) in a highly endemic population in southwestern Japan. As of August 1995, 1,960 individuals have been enrolled, of whom 27% were HTLV-I antibody positive at baseline. Our achievements over the past decade of following this cohort include the identification of several viral markers that characterize high-risk carriers and the documentation that carriers have subclinical evidence of impaired cellular immunity. We have begun to estimate the impact of the infection on the health of carriers and have found that men are at greater risk of HTLV-I-associated diseases than women. We have been able to identify prospectively risk factors associated with sexual transmission. Most important, by identifying subclinical markers of pathogenesis, we hope to provide the foundation for developing interventions to prevent HTLV-I-associated disease.

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Although it is thought that infection with human T‐lymphotropic virus type I (HTLV‐I) is immunosuppressive, this has not been clearly demonstrated among healthy carriers, and there are no data concerning delayed‐type hypersensitivity (DTH). To evaluate this hypothesis, DTH to purified protein derivative (PPD) of tuberculin was measured in 126 healthy adults from an endemic area for HTLV‐I infection in southern Japan. Among the 39 HTLV‐I carriers, only 15% had detectable induration following PPD exposure, compared to 46% of the 87 non‐carriers. In addition, the size of erythema among those carriers with a positive reaction was about 70% of that among non‐carriers. Overall, there was a significantly inverse association between the degree of DTH response and prevalence of antibody. In relation to subjects with strong to moderate reaction, those with negative or indefinite reaction were 6 times more likely to be a carrier. This association was much stronger among subjects aged 60 years or older than among younger persons. These findings indicate that there is subclinical immunosuppression among HTLV‐I carriers, which increases with age.

Specific antibodies to cell membrane antigens found on human T-cell leukemia virus (HTLV)-infected cells have been detected in Japanese patients with adult T-cell leukemia/lymphoma and in asymptomatic carriers, using a live cell-membrane immunofluorescence assay. Reactivity of the positive antisera was analyzed using radioimmunoprecipitation and NaDodSO4/PAGE with the HTLV-infected tumor cell line Hut 102 (clone B2). The major cell-associated antigens identified include two glycoproteins of -61 and 45 kDa, which appear to be the most immunogenic species in exposed people, a nonglycosylated species of 42 kDa, and four additional species that contain gag gene-encoded antigens with sizes ranging from 19 to 55 kDa. The two glycoproteins (gp6l and gp45) are encoded, at least in part, by the env gene of HTLV as evidenced by amino acid sequence analysis.