HUMAN IMMUNODEFICIENCY VIRUS (HIV)

 HUMAN IMMUNODEFICIENCY VIRUS 
(HIV) 

HIV is a retro virus having RNA as the genetic material. The virus attacks immune system of the host, eventually resulting in AIDS (Acquired Immunodeficiency Deficiency Syndrome). This immune-deficiency leads to development of opportunistic infections. Luc Montagnier, a French virologist was awarded Nobel Prize in 2008 for discovery of HIV. The virus kills CD4+ cells, and results in a decrease in CD4 counts, gradually progressing to AIDS. The virus is spherical in shape with a diameter of ~120nm. The outer envelope has spike like glycoproteins composed of proteins gp120 and gp41. Viral genome comprises two copies of single stranded RNA (ssRNA) that codes for nine genes. These include three structural genes: Group Specific Antigen (gag), Polymerase (pol) and Envelope (env). In addition to structural genes, HIV possesses genes whose products contribute to the complex regulation and replication of the virus, these are called as regulatory genes. Two major types of the viruses HIV type1 and HIV type 2 have been identified. The major serological differences between these types reside in the surface protein gp120. The two types are further divided into subtypes or ‘clades’ due to the marked variability in gp120 protein. The lipid bilayer is also studded with a number of host-cell proteins that the virus acquires during the budding process. HIV has a characteristic dense, cone-shaped nucleocapsidcomposed of the core protein p24. This nucleocapsid harbours two identical copies of the 9.8 kb single-stranded positive polarity RNA genome, associatedwith the viral enzymes reverse transcriptase (RT), RNase H, integrase and protease