Suppression of tuberculin skin reaction in healthy HTLV‐I carriers from Japan

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.