This chapter begins with a general introduction to viruses, including their common structural features, their dependence as obligate intracellular parasites on cellular metabolism, a typical virus infection life cycle, how viruses infect their host, and how we treat viral infections. This is followed by a section describing the properties of retroviruses, the class of virus to which HIV belongs. All retroviruses have two unique properties: they store genetic information in the viral particle as RNA, and, using an enzyme called reverse transcriptase, they can make DNA copies that are stably integrated into the host cell’s DNA. These unique features of retroviruses and the life cycle of a retrovirus are described in the text and illustrated diagrammatically. The three genes common to all retroviruses, gag, pol, and env, and the proteins they encode, are also described. Next is a comprehensive section on the properties HIV itself, which is identified as a member of a subgroup of retroviruses known as lentiviruses. The entry of HIV into cells using CD4 as a receptor, together with a coreceptor, either CCR5 or CXCR4, is described, providing an explanation for why helper T cells, which express CD4 and CXCR4, and macrophages which express CD4 and CCR5 are the cells infected by HIV. The extra genes contained in HIV including rev and tat are briefly described. This is followed by an introduction to the clinical consequences of HIV infection and drugs, such as AZT and protease inhibitors, that are used to treat AIDS that are discussed in more detail in Chapter 5.
The ELISA and Western blot tests for HIV infection are described and the fact that they test for antibodies against HIV that infected individuals produce is explained. Examples of how the HIV test can give false positives or false negatives are described. The concept of the polymerase chain reaction (PCR) to detect HIV in the blood and infected cells is also mentioned. There is also a discussion about the possible evolutionary origins of HIV.
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