Question of the Week

Biobasics Question of the Week:

How does the Human Immunodeficiency Virus (HIV) affect the Immune system?

Biobasics Solution:

The HIV belongs to a family of viruses called the Retroviruses characterized by the presence of RNA as genetic material. It is not acquired through intact skin or membranes, so the route of infection is either

§ Through direct injection of infected fluids (blood, plasma, medicines or other drugs) or,

§ Sharing infected needles or,

§ Sexual intercourse or,

§ Birth and breastfeeding by infected mothers (can also be transferred during pregnancy).

Life Cycle: Once inside the body, HIV is picked up by macrophages as a clearance mechanism of body. The virus soon produces copies of DNA from its genetic RNA by a process called reverse transcription. This viral DNA gets integrated to the host cell DNA and directs the cell to divide, hence producing 2 copies of viral DNA. This is followed by transcription and then translation to produce viral proteins. The latter are assembled to produce mature virions which are releases from host cell by budding from plasma membrane.

Impact on Immune cells: Infected macrophages and dendritic cells also carry the virus to nearby lymph nodes where the virus infects helper T cells (T_H) faster than they are replenished by the body, hence depleting their number. In the absence of adequate number of T_H cells, which are essential for activation of cytotoxic T (T_C) cells, the latter are not fully activated. T_c cells are body’s killer cells for HIV, so HI virus is able to survive because of lack of activated T_c cells infecting more and more immune cells causing severe immune deficiency.