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. Some have argued that AIDS and HIV have been around for thousands of years and we are simply seeing a reemergence of the scourge. We know from reading the hieroglyphics on the temple and pyramid walls of ancient Egypt that the Egyptians of nearly five thousand years ago had a similar epidemic where people mysteriously died of immunosuppressive (weakening the immune system) disorders very much like what we see today in AIDS patients. But today we know that HIV mutates very rapidly, changing about 1 percent each year. It is likely that throughout human history, infectious diseases that were highly virulent and immunosuppressive emerged, killing many thousands, and then subsided. A virus that weakens the immune system opens the way for the same kinds of opportunistic infections and cancers that occur in people with AIDS. In other words, the disease would be AIDS-like but not AIDS itself, caused by an HIV-like agent but not HIV itself.
Some have claimed that HIV was artificially created in a biological warfare laboratory and purposely released in the population to kill off gay men, injecting drug users, Haitians, and Africans. Near the end of the Cold War in the mid-1980s, the then Soviet Union went so far as to claim that HIV was invented and released just for that purpose from a biological warfare lab in Maryland. The United States Department of State spent much time and effort to counter that argument around the world, insisting there was no truth to the allegation. But could it