Abstract
The study objective was to evaluate the effects of long-term methadone use and human T-cell leukemia virus (HTLV) types I and II seropositivity on the distribution of lymphocyte subsets and on lymphocyte function as measured
in vitro in intravenous drug users seronegative for human immunodeficiency virus type 1 (HIV-1).
Anti-HIV-1-negative intravenous drug users receiving methadone maintenance therapy (n = 24) were studied in a Veterans Administration drug abuse treatment center. These subjects were compared to 38 age-and sex-matched control subjects who did not abuse drugs. HIV-1 and HTLV serostatus was determined by repetitive enzyme-linked immun-osorbent assay and confirmed by immunoblot. Lymphocyte subsets were determined by two-color flow cytometry. Lymphocyte function was measured by proliferative response to plant mitogens and by natural killer (NK) cell-mediated cytotoxicity to a tumor cell target.
Significant differences were seen in lymphocyte phenotype in the methadone-treated group, with elevations in the T-cell helper sub-set CD4+CD29+; in CD8 and CD8+I2+ cells, suppressor/cytotoxic T lymphocytes, and activated suppressor/cytotoxic T cells; and in CD2+CD26+ cells and activated total T lymphocytes. Lymphocyte function was suppressed in the methadone group, with poor responses to pokeweed mitogen and phytohemagglutinin in culture. Moreover, NK-cell cytotoxicity was significantly reduced in the methadone group. None of these immunologic differences were attributable to HTLV serostatus.
The immune abnormalities seen suggest that a clinically significant degree of immune impairment exists in methadone-treated intravenous drug users. However, these abnormalities could not be explained by the presence of other retroviruses in this HIV-1-negative study group, as there was no significant difference in immune function when HTLV-seropositive patients were compared to HTLV-seronegative subjects treated with methadone.
