ObjectivesTo determine the effect of retrovirus infection and co-infection, and intravenous substance use, on immune function in African-Americans.DesignA cohort of South Florida street-recruited African-American intravenous drug users formed the study population. The cohort consisted of 90 HIV-negative & human T-lymphotropic virus (HTLV)-negative, one HIV-negative & HTLV-I-positive, 11 HIV-negative & HTLV-II-positive, 79 HIV-positive & HTLV-negative, one HIV-positive & HTLV-I-positive and 21 HIV-positive & HTLV-II-positive individuals. The results reported are for the cross-sectional, baseline assessment of immune parameters.MethodsLymphocyte phenotypic distributions and functional markers, including proliferative response to mitogens and natural killer cell cytotoxicity, were determined. Serum immunoglobulin (lg) levels were determined as a measure of B-cell activity.ResultsHTLV-II infection was associated with increases in CD8 lymphocyte count and serum lg, but with no other significant immunologic changes. The distribution of CD4 and CD8 percentages, CD4: CD8 ratio, phytohemagglutinin (PHA) and pokeweed mitogen (PWM) reactivity, lgA and lgG for the four retrovirus serostatus groups suggested the possibility of interactive effects in the co-infected group, as demonstrated by a trend toward lower medians for CD4 and for PHA and PWM response and higher medians for lgC, lgA and CD8. Retrovirus-seronegative intravenous drug users had significantly impaired immune status compared with non-drug-using control individuals.ConclusionsImmunologic dysfunction attributable to HTLV-II infection was minor compared with HIV infection in this population. Study subjects who were co-infected with HIV and HTLV demonstrated more impairment of immune function than individuals with single retrovirus infections.