HIV damages the body's immune system and makes it susceptible to infections and certain types of cancers. A single HIV viral particle is called virion. The viron is surrounded by the viral envelope which contains the proteins gp120 and gp41. The matrix lies below the viral envelope. The capsid is the viral core and houses HIVs genetic material (RNA) and the enzymes required for viral replication. HIV is a retrovirus, therefore it is capable of copying RNA into DNA. The enzymes required for HIV viral replication are reverse transcriptase, integrase and protease.
HIV Infects and Destroys T Helper Cells
The major steps in the HIV infection and replication cycle are attachment, entry, reverse transcription, integration, protein processing and maturation. Gp 120 is a protein present on the viral envelope. This protein binds to the CD4 receptor that is present on T-helper cells. Once the virus enters the T-helper cell, it is uncoated and the viral RNA undergoes reverse transcription to become proviral DNA. This DNA is transported into the T cell nucleus. The HIV integrase enzyme then incorporates the proviral DNA into the T-helper cell genome. When the provirus is activated, HIV viral polyproteins are expressed using the T-helper cell machinery. Polyproteins are cleaved by the HIV protease enzyme and the virion buds from the host cell. The budding process destroys the T cell. The T cell can also be destroyed when the virus overwhelms the host T cell machinery. Mature viral particles go on to infect more cells..
HIV Affects B Cells and CD8 T Cells
T helper cells are involved in helping B cells make antibodies. The CD8 T cells, also called cytotoxic T cells, are involved in killing virally infected or damaged cells. As HIV replicates it continues to destroy CD4 T-helper cells. Over time, HIV infection leads to a significant reduction in the number of CD4 T helper cells. Since CD4 T helper cells are needed to activate B cells and cytotoxic T cells elicit an immune response, the destruction of these cells weakens the immune system.
HIV Affects Macrophages
Macrophages are large immune cells that engulf and digest invading microorganisms and also scavenge damaged cells, dead cells and cellular debris. Macrophages play a crucial role in HIV infection and are the first cells infected by HIV. They also serve as the source of HIV production when CD4 T cells are depleted.
References
- Joint United Nations Programme on HIV/AIDS (UNAIDS) and World Health Organization (WHO); AIDS epidemic update
- "Nature"; 25 years of HIV; Anthony S Fauci; May 2008
