Human immunodeficiency virus (HIV) is an RNA retro-helper CD4T cells, reducing the number of helper T cells virus; it contains an enzyme called reverse transcriptase. HIV is the virus that causes acquired immunodeficiency syndrome (AIDS). It has an incubation period that may be as long as 11 years before symptoms of clinical AIDS occur. The great majority of HIV-infected individuals eventually develop AIDS. HIV gains entry to helper T cells by binding to CD4 molecules. The virus then injects its own genetic information into the cell cytoplasm (Fig. F14.3.1). This injected genetic information consists of single-stranded RNA. The viral RNA is incorporated into the infected T-cell genome through reverse transcription of the RNA into DNA. The transcribed DNA is then incorporated into the host DNA. The T cell then makes copies of the virus, which are extruded from the T cell through exocytosis. These HIV particles then infect other helper T cells. The immune system responds to this condition by generating cytotoxic CD8 T cells and antibodies directed against the virus particles. Cytotoxic CD8 T cells kill HIV-infected (the helper T-cell count is actually used as a clinical indicator of the progress of HIV infection). As the helper CD4 T-cell population becomes depleted, infected individuals eventually become incapable of generating an immune response against bacterial or viral infections. They usually die of secondary infections caused by opportunistic microorganisms or cancer.
Anti-HIV treatment is the major strategy against HIV infection and AIDS. Azidothymidine (AZT), an inhibitor of reverse transcriptase, was the first promising drug used to treat HIV infection. Currently, the most effective treatment is multiple drug therapy known as highly active antiretroviral therapy (HAART), which uses a combination of several chemotherapeutic agents. These include nucleoside and nonnucleoside reverse transcriptase inhibitors and HIV protease inhibitors. HAART offers several advantages over monotherapy such as synergistic dosage effects and reduced side effects as well as reduced drug resistance.
FIGURE F14.3.1 • Schematic diagram of the interaction between HIV and the helper CD4T cell. Human immu -nodeficiency virus (HIV) is the RNA virus that causes AIDS. It contains reverse transcriptase. HIV gains entry into the helper CD4T lymphocyte by binding to the CD4 molecule and injecting its genetic information into the cell cytoplasm. Accessory cell surface molecules such as gp 120 assist in viral entry into the cell. These proteins interact with CD4 molecules. The injected genetic information is incorporated into the host cell genome through reverse transcription of RNA into DNA. This DNA containing viral information is then incorporated into host DNA. HIV HIV gp 120 gp 120 CD4 CD4 chemokine receptor chemokine receptor gp 41 gp 41 RNA RNACD4T lymphocyte