Q.AIDS is not a disease. But it facilitates the attack by other organisms. Why ?

HIV destroys helper T (CD4+) lymphocytes, progressively collapsing the immune system, so AIDS patients become vulnerable to and usually die from opportunistic infections and cancers rather than from HIV itself.

HIV selectively infects and replicates within helper T-lymphocytes (CD4+ T cells), which are central to the immune system because they help activate B-cells (for antibody production) and cytotoxic T-cells (for killing infected cells), essentially acting as coordinators of the adaptive immune response. Over the course of infection, HIV progressively destroys these helper T cells (through direct viral lysis and other mechanisms), causing their number in the blood to steadily decline. As helper T cell numbers fall below a critical threshold, the body's ability to mount both cell-mediated and, indirectly, humoral immune responses collapses, a state termed immunodeficiency. Because a severely weakened immune system can no longer control microorganisms that a healthy person would easily fight off, AIDS patients become susceptible to a wide range of 'opportunistic' infections and diseases — such as persistent fungal infections, tuberculosis, unusual pneumonias (e.g. caused by Pneumocystis), severe diarrhoeal disease, and certain cancers (like Kaposi's sarcoma) — that rarely cause serious illness in people with normal immunity. It is these secondary opportunistic infections and cancers, explo …