Decreased reactivity to PPD among htlv‐i carriers in relation to virus and hematologic status

Data on human T‐cell lymphotropic‐virus‐type‐1 (HTLV‐I) status and hematology from 528 individuals were analyzed for associations with low reactivity to the purified protein derivative (PPD) of Mycobacterium tuberculosis recall antigen. Subjects were classified as HTLV‐I carriers with abnormal lymphocytes (Ably), carriers without Ably, and seronegatives. All carriers had a significant 2.6‐fold risk of being low responders to PPD compared with the seronegatives, carriers with Ably having the highest relative risk. Carriers with HTLV‐I‐antibody titer 1:256, or with other detectable markers of virus status such as antibody to tax and proviral DNA, had increased risk for low response to PPD similar to the estimate for HTLV‐I seropositivity alone, compared with the seronegatives. Subjects with a low lymphocyte count had 3.5 times the risk for being low responders to PPD, compared with subjects with high counts. Similarly, subjects with a low monocyte count had 2.0 times the risk for low reactivity of those with a moderate to high count. Results were not confounded by age, sex, smoking or alcohol drinking. Using multiple logistic regression, only HTLV‐I seropositivity and low lymphocyte and monocyte counts were predictive of low reactivity to PPD. Analysis indicates that suppression of delayed‐type hypersensitivity is associated with HTLV‐I infection per se, and not with viral replication or load. Furthermore, this effect may occur in part via changes in the number and function of lymphocytes and monocytes. Such a mechanism may involve altered cytokine production in carriers and concomitant changes in cell populations involved in delayed‐type hypersensitivity.