CD8 T lymphocyte subset markers and HIV infection

Activation of tumor necrosis factor--alpha system in HIV-1 infection: association with markers of immune activation

The relationships between serum levels of soluble tumor necrosis factor receptors (sTNFRs) and other prognostic and immunological parameters in different immunological subgroups of 64 HIV-1 infected patients were studied. In the patient group as a whole, the raised serum levels of sTNFRs were significantly inversely correlated to the numbers of CD4+ and CD8+ lymphocytes and significantly positively correlated with serum levels of neopterin, HIV-1 p24 antigen and the soluble CD8/CD8+ lymphocyte ratio. However, when the patients were classified into three separate immunological subgroups according to the numbers of CD4+ lymphocytes, only serum levels of neopterin were significantly correlated to levels of sTNFRs in all the defined immunological subgroups. These results indicate that HIV-1 infection is associated with a persistent and chronic immune activation in the TNF system manifested by raised serum levels of sTNFRs, which may reflect sustained activation of the immune system particularly in monocytes/macrophages. Further, these results confirm that, when comparing immunological and virological parameters in HIV-1 infection, different results may be obtained in different immunological subgroups of patients.

Cytotoxic T lymphocyte activity and CD8 subpopulations in children at risk of HIV infection

HIV-specific cytotoxic T lymphocytes (CTL) are thought to play a major role in viral control in HIV-infected adults. Changes in the relative proportions of CD8 lymphocyte subpopulations are also thought to be associated with disease progression. Less is known about the relative effectiveness of CTL against different HIV targets, or about the relationship, if any, between CTL activity and CD8 subpopulations. We have measured CTL activity against four HIV gene products (gag, tat, pol and env) and expression of CD45RO, CD45RA, HLA-DR, CD29, S6F1, and CD57 surface markers on CD8 cells from nine HIV-infected and 11 HIV-uninfected children. Of nine HIV-infected children, six showed antigen-specific CTL activity on at least one occasion: 4/6 directed against tat, 6/6 against pol, 1/6 against env, and 1/6 against gag. However, the specificity of the CTL activity varied between children and within individual children with time. Furthermore, two uninfected children showed CTL activity, one to HIV-gag, -pol and -tat, and the other to HIV-pol. All the HIV-infected and two uninfected children had abnormal proportions of CD8 subpopulations in whole blood compared with age-matched controls. There was no correlation between CTL activity and CD8 subsets in whole blood. Five children changed from CTL-positive to CTL-negative (or vice versa) during the study. In these, the occasions when CTL activity was detected coincided with an increase in CD8 cells, an expansion of HLA-DR+ CD8 cells and a loss of CD45RA+ CD8 cells.

Immunobiological aspects of HIV treatment

Recent information on the efficacy of anti-retroviral therapy and vaccination strategies has been disappointing as well as confusing. The recently announced Concorde study suggested that there is no advantage to early treatment of asymptomatic HIV infection with azidothymidine alone, even though the levels of CD4+ cells in the treated group were consistently higher than in the untreated group. This will lead to increasing attention being paid to the mechanisms whereby HIV causes AIDS, which have sadly been sidelined in the rush to produce classically based therapies and vaccines. Over the last year many different theories on how HIV kills CD4+ cells and leads to AIDS have been discussed and tentatively explored.

Phenotypic characterization of CD8+ T cell populations in HIV disease and in anti-HIV immunity

The CD8+ T cell population is believed to play an important role in the control of viral infection, both for suppression of viral replication and for cytotoxic activity against viral infected cells. Elevated numbers of CD8+ T cells have been demonstrated in HIV infection, and CD8+ cytotoxic T cell (CTL) activity is associated with the early, asymptomatic stage of disease. We investigated the phenotypic characteristics of the CD8 population, in whole blood, in HIV disease and determined the predominant CD8+ subpopulation involved in anti-HIV CTL activity. We found that CD8+ T cells co-expressing markers of activation (HLA-DR), memory (CD45RO, CD29), and cytotoxic activity (S6F1) were significantly elevated in the early stages of disease, while the numbers of naive (CD45RA) cells remained unchanged. Progression to AIDS resulted in an overall loss of absolute CD8+ T cells, though the percentages of CD8+ HLA-DR+ and CD8+ S6F1+ remained elevated. In contrast to patients in the late stages of disease, anti-HIVgag CTL activity, following in vitro stimulation, was present in most HIV+ asymptomatic subjects and was associated with an expansion of CD8+ HLA-DR+ and CD8+ CD45RO+ cells. The absence of CTL activity was associated with a reduced ability of these populations to expand in vitro and with a significant loss of peripheral CD4+ T cells, independent of clinical stage. We suggest that CD8+ expressing HLA-DR+ CD45RO+ and S6F1+ play an important role in anti-HIV cytotoxicity.