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HIV mainly infects cells bearing the CD4 surface molecule, which acts as a specific receptor for the viral envelope protein, gp120. Such cells are found predominantly within the immune system and include T-helper lymphocytes, monocytes and antigen-presenting cells.


This CD4-defined tissue tropism explains the major pathological effects of HIV, which are immunodeficiency and neurological disease. However, HIV may also cause damage at sites where CD4 is not expressed. This may be a result of direct infection of CD4-cells, in which low levels of viral replication can occasionally occur, or due to infiltration of tissue by HIV-infected lymphocytes and macrophages, which release toxic viral proteins and/or pro-inflammatory cytokines. (Nye & Paskin, 1994:41)
There have been a lot of unusual theories attempting to explain the origin of AIDS. Some people have theorized that it began in rural Haiti and spread to urban Haiti, and then to gay men in the United States and to Africans in Kinshasa, Zaire (the capital of that central African nation), where many Haitians were living. This theory is no longer accepted, since HIV research in rural Haiti shows that HIV was very rare there, and that it has been spreading from urban Haiti to rural Haiti, not the other way around. HIV in the late 1970s and early 1980s was more likely to have spread into Haiti from gay men coming from the United States to bisexual male Haitians, and from HIV-infected Haitian men and women returning from Zaire to persons living in Haiti. ...
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