HIV

HIV

HIV is virus that belongs to retroviruses and more specifically to lentiviruses, is enveloped and contains two RNA strains with positive polarity. His genome is composed by 9 genes clasificated in 3 groups: structural genes: gag, pol, env; regulatory genes: tat, rev; accessory genes: vpr, vpu, vif and nef. Gag genes code for core proteins which consists of p24, p17 and p7. Env codes for envelope proteins which consists of gp120 (surface protein) and gp41 (transmembrane protein). Pol codes for protease, integrase and reverse transciptase.

Tat gene codes for a genome binding protein that ensures the full-transcription of the viral genome, and rev is a protein that allos virus pass through early to late phase, this protein links immature ARN without splicing and take it outside nucleus.

Nef genes encode a protein that inhibits CD4+ and MHC-1, vpr is a transporter protein that inserts itself in every cell membrane, allowing virus infect non-dividing cells, translocate the preintegration complex through the nucleus and eliciting apoptosis by his insertion in the mitochondrial membrane. Vif are essencial for viral transcription and VPU destroy the CD4+ like Nef.

Infection

The infection occurs in every cell with CD4+ and co receptor: CCR5 or CXCR4 in macrophages or lymphocytes respectively. But the first contact is with the DC via DC-sign this cell carry the virus to a lymphatic node where meets the susceptible cells. The gp 120 links the CD4+ and the co receptor and change the conformation allowing the gp41 bring the hydrophobic domain for membrane fusion. When the virus enter the cells is decapsidated and laves the RNA and constitutional proteins in the cytoplasm, the reverse transcriptase converse the RNA to DNA, then the integrase cuts the genome limits allowing the insertion in the host genome, where the protease cut the new RNAm in small peptides that constitutes the viral proteins. The viral genome replicates and destroys the host cell bringing new virions.

There are two types of HIV phenotypes: R5 and X4, R5 occurs when the virus infects first macrophages and X4 when infects lymphocytes. X4 is more aggressive and develop very quickly toward AIDS.

The pathogenesis is explained by cell lysis and the mechanisms are three: apoptosis, depletion by immune system and delayed lymphocytes regeneration.