Expression Patterns of Phenotypic Markers on Lymphocytes from Human Immunodeficiency Virus Type 2-Infected Baboons

The development of AIDS in HIV-1-infected humans is associated with profound changes in the expression patterns of lymphocyte phenotypic markers associated with increased immune activation and with decreased recall immune responses. In assessing these immunologic changes in an animal model, we characterized the expression patterns of immune activation markers on lymphocyte subsets during the acute, chronic, and end stages of HIV-2 infection in baboons. Using flow cytometry, we identified 21 human-specific monoclonal antibodies that were cross-reactive with baboon lymphocytes; however, expression of only 2 of these markers was altered significantly after HIV-2 infection. We found an increase in baboon class II antigen (as measured by anti-HLA-DR) in the CD4⁺ T cell subset within 8 weeks of infection(p = 0.045). Moreover, after 1 year of infection, CD11b was downregulated on CD8⁺ T lymphocytes (p = 0.027). This downregulation of CD11b was consistently observed in all of the groups of baboons that were chronically infected with three different HIV-2 isolates. In addition, we found substantial downregulation of the interleukin 2 receptor (CD25) and upregulation of class II antigen on CD8⁺ lymphocytes in a baboon with an AIDS-like disease. These and other phenotypic markers of immune activation may facilitate characterization of the immunopathogenesis of AIDS in nonhuman primate animal models.