Human immunodeficiency viruses replicate mostly in T helper cells. They do this by reprogramming the metabolism of the infected cell in such a way that they replicate, whereas the infected cell perishes.
As T helper cells play an important role in the immune response, the infected person’s immune system becomes progressively weaker. Eventually, the immune system collapses, with the result that relatively harmless pathogens can give rise to life-threatening opportunistic infections. These include:

• fungal infections (e.g. candidiasis, Pneumocystis carinii pneumonia)
• viral infections (e.g. herpes, cytomegalovirus)
• cancers (e.g. Kaposi’s sarcoma, lymphomas, cervical cancer)