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Human immunodeficiency virus (HIV) is the cause of acquired immunodeficiency syndrome (AIDS).
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Both HIV-1 and HIV-2 cause AIDS, but HIV-1 is found worldwide, whereas HIV-2 is found primarily in West Africa. This chapter refers to HIV-1 unless otherwise noted.
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HIV is one of the two important human T-cell lymphotropic retroviruses (human T-cell leukemia virus is the other). HIV preferentially infects and kills helper (CD4) T lymphocytes, resulting in the loss of cell-mediated immunity and a high probability that the host will develop opportunistic infections. Other cells (e.g., macrophages and monocytes) that have CD4 proteins on their surfaces can be infected also.
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HIV belongs to the lentivirus subgroup of retroviruses, which cause “slow” infections with long incubation periods (see Chapter 44). HIV has a cylinder-shaped (type D) core surrounded by an envelope containing virus-specific glycoproteins (gp120 and gp41) (Figures 45–1 and 45–2). The genome of HIV consists of two identical molecules of single-stranded, positive-polarity RNA and is said to be diploid. (Note that this is not double-stranded RNA, which consists of one positive strand and one negative strand.)
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The HIV genome is the most complex of the known retroviruses (Figure 45–3). In addition to the three typical retroviral genes gag, pol, and env, which encode the structural proteins, the genome RNA has six regulatory genes (Table 45–1). Two of these regulatory genes, tat and rev, are required for replication, and the other four, nef, vif, vpr, and vpu, are not required for replication and are termed “accessory” ...