Low T-lymphocyte ratios in homosexual men. Epidemiologic evidence for a transmissible agent.

To investigate risk factors for immunologic abnormalities among homosexual men, T-lymphocyte helper/suppressor (OKT4/OKT8) ratios were determined in 78 healthy Danish homosexual men. Ratios in 26 men (33%) were low (less than 1.00). Visiting the United States in 1980 to 1981 was a strong (7.7-fold) risk factor for having a ratio less than 1.00. Among nine travelers who visited only once, the risk of having a low ratio increased significantly if the visit had occurred in 1981. A risk of similar magnitude (6.9-fold) was found among the three men who had not been to the United States but who reported homosexual contact with a Danish man who became ill with Kaposi's sarcoma. Risk of low ratios did not correlate with age or years of homosexual activity. Promiscuity was not a significant risk factor, but these men generally had fewer sex partners than that which has been reported from the United States. Neither nitrite inhalant use nor cytomegalovirus antibody (prevalence or titer) was associated with low ratios. These data support the hypothesis that a transmissible biologic agent may be etiologically responsible for the low helper/suppressor ratios in homosexual men.