38.2 Pathogenesis of HIV infection and AIDS

HIV infection begins as an acute form and with slow progression changes to chronic form. Memory CD4+ T cells get infected and there is depletion of lymphocytes. Progression of disease from acute to chronic form is indicated by dissemination of the virus, viremia and the development of host immune responses. Besides CD4+ T cells, macrophages and dendritic cells also get affected. In later stages, lymph nodes and spleen become the targeted replication sites for the virus.

38.3 Mechanisms of immunodeficiency caused by HIV

Obviously HIV impairs both adaptive and innate immune system but cell mediated immunity gets affected markedly. Diminishing of CD4+ T cells in HIV infected patients is the result of cytopathic effect of the virus. The lysis of CD4+ T cells may occur due to the increased plasma membrane permeability and the flow of lethal amounts of calcium leading to apoptosis. Possibly it may also happen that viral production hampers cellular protein synthesis thereby causing cell death. Other reasons of reduction in lymphocytes would be loss of function of CD4+ T cells in the infected patients.

38.4 Mechanism of immune evasion by HIV

HIV is a dreaded disease. It has a high mutation rate because of its genome content and thus it may evade any antibody response. MHC class I molecules may have some role in its immunity which can be confirmed by evasion of CTLs through down-regulation of MHC I molecules.

 

Figure 38.1 Diagram showing mechanism of acquired immunodeficiencies: