HUMAN IMMUNODEFICIENCY VIRUS AND LIFE CYCLE
HUMAN IMMUNODEFICIENCY VIRUS (HIV)
HIV is a lentivirus, which is characterized as a member of the retrovirus family that causes Acquired Immuno Deficiency Syndrome (AIDS). (1)
Lentiviruses are the viruses that have ablility to infect non-cycling cells. (2)
AIDS is a condition in humans during which the immune system begins to fail due to decrease in the number of T cells.
Thus AIDS leads to life-threatening opportunistic infections .Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk.
CD4 Cells and Cause Of HIV
As the HIP progress in a patient the CD4 cells become the host cells that helps in the HIV replication. Thus the HIV get attached to the CD4 cells, this allows the virus to enter and infect the CD4 cells and thus leads to the further damage of the immune system. (3)
There are two primary types of T-cells and their role :
CD4 Cells - These cells have molecules called CD4 on its surface. These cells thus prevent the growth of the microorganisms inside the body.
* CD8 Cells - T-cells have a molecule called CD8 on their surface. CD8 cells destroy cells that have been infected with foreign invading micro-organisms.
CD4 CELLS COUNT IN BODY
Normal CD4+ T lymphocyte counts are about 750/microL.
When this count get decreased to 500/microL the body is found to be infected .
The immune system get severely weak when this count get less than 200 and the HIV+ person is at a much greater risk of opportunistic infections. (4)
HIV LIFE CYCLE (5)
Step 1 - HIV has proteins on its envelope that are strongly attracted to the CD4+ surface receptor on the outside of the T4-cell.
Step 2 - After the binding process, the viral capsid (the inside of the virus which contains the RNA and important enzymes) is released into the host cell.
Step 3 - A viral enzyme called reverse transcriptase makes a DNA copy of the RNA.
Step 4- Then, another viral enzyme called integrase hides the proviral DNA into the cell's DNA.
Step 5 - The strands of viral DNA in the nucleus separate, and special enzymes create a complementary strand of genetic material called messenger RNA or mRNA.
Step 6 - The mRNA carries instructions for making new viral proteins from the nucleus. The final step begins with the assembly of new virus. Long strings of proteins are cut up by a viral enzyme called protease into smaller proteins. These proteins serve a variety of functions. (3)