AIDS
Probably the most recognised feature of the immune response which causes problems is that of immunodeficiency, and the prime example of this is HIV/AIDS. The HIV virus enters the CD4+ cell, loses it's coat, and a single stranded DNA copy of the viral RNA is made by the viral enzyme HIV reverse transcriptase. A complementary DNA strand is then produced giving a replication of the virus and incorporates into the host genome. When an infected T cell is activated, infectious viral particles are produced which overcome the hosts defence mechanisms and progressively infect more T cells which die off and decrease in numbers. Polyclonal B cell activation also occurs causing a large increase in IgG. Because of the immune systems natural response to infection the virus is spread throughout the system. Eventually, after massive losses of CD4+ cells, the HIV virus turns into AIDS.
Cancer
Tumour cells have a number of surface structures which the immune system can recognise as antigenic. …
