New insights into the immune pathway leading to progression of HIV infection

Although a major problem of immune system during HIV infection is thought to be related to infection of key immunocompetent cells such as CD4+ lymphocytes and phagocyte, the strong immune dysfunction paralleling the development of HIV infection mainly concerns also apparent discrepancies regarding the roles played by CD8+ T lymphocytes. Insights over this important problem were recently gained by single cell analysis of different CD8+ subpopulations, both in progressive evolutionary stages of the infection and by longitudinal studies. It was possible, in such a way, to envisage the following immune pathways leading to progression of HIV infection. In early stages a protective, ″non-cytotoxic″ response presumably prevails, sustained by the CD8+ CD28+ subpopulation, which is able both to control HIV replication within CD4+ infected cells and to avoid possible dangerous attacks by cytotoxic cells. In late stages cytolytic responses progressively prevail, possibly mediated by CD8+ CD28+ subpopulation and amplified by the CB8+ subpopulation releasing IFNγ, against not only CD4+ infected cells, but also non-infected cells. Thus a pathway mediated by action of different CD8+ subpopulations may contribute to explain the development of HIV infection