OPERATION OF HIV:
How HIV Specifically Affects the Immune SystemRemember about the proteins, which are part of the envelope of HIV?
Well, one of these proteins, named gp 120, (a sugar-containing protein called a glycoprotein, of approximately 120,000 molecular weight), "recognizes" a protein on helper T-cells named CD4, and physically associates with it. The CD4 [Cluster of Differentiation Antigen No. 4]
Thus, CD4 is a specific receptor for HIV. This virus however, can also infect other cells which include macrophages and certain other kinds of cells which can engulf substances through a process known as phagocytosis. As a consequence of the interaction with CD4 on helper T-cells, HIV specifically infects the very cells necessary to activate both B-cell and cytotoxic T-cell immune responses. Without helper T-cells, the body cannot make antibodies properly, nor can infected cells containing HIV (an intracellular pathogen) be properly eliminated. Consequently, the virus can: multiply, kill the helper T-cell in which it lives, infect adjacent helper T-cells, repeat the cycle, and on and on, until eventually there is a substantial loss of helper T-cells.
The fight between the virus and the immune system for supremacy is continuous. Our body responds to this onslaught through production of more T-cells, some of which mature to become helper T-cells. The virus eventually infects these targets and eliminates them, too. More T-cells are produced; these too become infected, and are killed by the virus. This fight may continue for up to ten years before the body eventually succumbs, apparently because of the inability to any-longer produce T-cells. This loss of helper T-cells finally results in the complete inability of our body to ward-off even the weakest of organisms (all kinds of bacteria and viruses other than HIV) which are normally not ever a problem to us. This acquired condition of immunodeficiency is called, AIDS.
