Three components of our defense against microbial infection.
1) The first line of defense is external and involves the skin and the mucous membranes. In case of HIV infection these barriers are very important because the HIV virus needs to penetrate into our body in order to infect its target cells. This is one of the characteristic of the HIV infection, at the difference of airborne viruses like the influenza virus, which gives us flu. HIV infection occurs when the HIV virus is in contact with infected blood or infected semen. It is also why it is extremely easy to be protected against an HIV infection. (involved in HIV infection)
2) The second line of defense is internal and nonspecific. This response does not require specificity, meaning that the cells involved in the response: Phagocytes (destroy microbes by phagocyting them, by digesting them) and Natural killer cells (destroy infected cells) act on a broad range of microbes without any kind of memory. This second line of defense is almost irrelevant in case of an HIV infection but involved in the immune response following an HIV infection (Acquisition of memory starts here too)
3) The third line of defense is internal and specific. It is the specific immune response. This response can be divided into 2 arms: The humoral response involving formation of antibodies by the lymphocytes B and the cell-mediated response involving the formation of a complex network of lymphocytes. This third line of defense is 100% involved in HIV infection and and immune response against HIV infection. I will come back later on the lecture to explain how the immune system responds to an HIV infection.
HIV AND AIDS
HIV (human immonodeficiency virus) is the name of the virus which cause AIDS (acquired immunodeficiency syndrome). Someone can be HIV infected and yet not show the AIDS symptoms. Differently, someone who has AIDS is someone HIV infected and at the terminal phase of his infection when opportunistics diseases develop because of the failure of the immune system. These diseases will be then responsible of the death of the patient. The HIV infected phase can last 15 years (at the most know so far. It might last longer but we do not have enough information timewise to tell yet. In addition this number varies individual to individual. Some people can leave this HIV infected phase for less than 5 years (2 years example) and some can leave 15 years. The common opportunistic diseases are pneumonia and Kaposi's sarcoma (skin cancer). And it is actually because of the increase of this rare, in the case of the Kaposi's sarcoma, or almost eradicated, in the case of pneumonia, among the population that scientists found that all these people had in common a failure in their immune system and particularly a major decline of their lymphocytes T helpers. That was back in 1981, but they did not know yet what caused these opportunistics diseases to develop. The discovery of HIV virus was made in 1984 by a french scientist named Luc Montagnier. I do not want to enter into the polemic but at this time there was a major fight between an american scientist, Robert Gallo and Luc Montagnier. Gallo claimed that he was the first to have discovered the virus responsible of AIDS. After a long series of arguments the discovery was attributed to Luc Montagnier.
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