HIV is transmitted by contaminated bodily fluids such as blood, semen and vaginal secretions. The virus attacks the immune system and causes it to gradually weaken until the patient develops AIDS.
Viruses
HIV belongs to a class of viruses known as lentiviruses, according to the National Institute of Allergy and Infectious Diseases. HIV is not itself a cell; instead it is a collection of infectious proteins and genetic material. Viruses are only able to reproduce when they are inside another cell. HIV is a retrovirus, which means that its genetic material is initially stored as RNA. Once it infects a cell, the virus converts this RNA into DNA, which is the genetic material used in human cells, and then uses the cell to make new copies of itself.
Immune System
HIV is unique in that it infects cells within the immune system. Part of the immune system is comprised of specialized cells called white blood cells or lymphocytes. Lymphocytes can be divided into two types of cells: B cells, which make specialized proteins called antibodies, and T cells, which stimulate the immune system in response to infections. HIV targets a specific subset of T cells that causes it to gradually weaken the immune system.
CD4 Positive T cells
HIV infects a type of cell known as a CD4 positive T cell, according to AIDS.org. These cells are also known as helper T cells because they make chemicals that help activate the immune system to fight an infection. These helper T cells have a protein on their surface that is called CD4. HIV needs to bind to this protein in order to enter the cell. Consequently, an HIV-infected cell is a CD4 positive T cell.
HIV Life Cycle
There are a number of steps involved in the infection of a CD4 positive T cell with HIV, according to AIDSInfo. The virus must first bind to the CD4 protein, as well as other proteins on the cell's surface. Once the virus has entered the cell, it converts its RNA into DNA and inserts this viral DNA into the T cell's genes. The T cell then makes copies of the viral genes and proteins. HIV then packages these proteins into new copies of itself and then escapes the T cell via a process known as budding.
T Cell Death
The viral infection of T cells may not directly be responsible for their death, according to a 2002 article in Nature Medicine, titled "CD4+ T-cell depletion in HIV infection: Are we closer to understanding the cause?" This article suggests that the main damage to T cells may not be a direct result of viral infection; instead, the presence of HIV may overstimulate helper T cells. When helper T cells are activated, they rapidly reproduce but then die off shortly thereafter. According to the article, HIV stimulates the immune system, leading not only to the rapid death of helper T cells, but also increased proliferation of the virus.
