Pathogenesis of AIDS

Abstract

The most important effector systems of the immune defense (production of antibodies, CTL, NK cells, monocytes/macrophages) require the assistance of helper T-cells which exhibit the surface marker CD4 (also called T4). This assistance consists of lymphokines produced and secreted by T4-cells, most importantly IL-2 and gamma interferon (IFN). T4-cells produce and secrete these lymphokines only when they themselves are activated. Under natural circumstances, activation results from presentation of a foreign antigen (from viruses, bacteria, fungi). These pathogens, or antigens of them, are ingested, partly degraded, and modified (processed) by monocytes/macrophages and other antigen-presenting cells (APC). Processed antigen is then expressed at their surface in conjunction with MHC class II (MHC-II). The antigen/MHC-II complex is recognized by the antigen receptor of the T4-cell. For activation, a second signal is required in the form of IL-1 secreted by the APC. In addition, the close contact required for these recognition processes depends on the interaction of the CD4 molecule with the nonpolymorphic beta₁ domain of MHC-II (Golding et al. 1986). These processes are schematically presented in Fig 14.