Hiv Aids

Introduction

Human Immunodeficiency virus(HIV)infection causes, immunodeficiency leading to Acquired immunodeficiency syndrome ( AIDS) , characterised by profound immunosuppression predisposition to opportunistic infections , aggressive form of cancer such as Kaposi,s sarcoma and B cell Lymphoma , wasting and central nervous system degeneration. This is one of the major killer diseases worldwide.

HIV is a retrovirus. HIV-1 is most common cause of AIDS. HIV- 2 causes similar clinical syndrome and endemic to western Africa.

Structure and Life cycle of Virus

The HIV virus is around 20nm in diameter and almost spherical shape. HIV-1 consists of two identical strands of RNA (viral genome) and enzymes reverse transcriptase, integrase, and protease, packaged in core composed of p24 capsid protein with a surrounding of p17 protein matrix. All surrounded by an envelope, consist of phospholipid bilayer derived from host and virus specific membrane proteins gp41, gp120.

Long terminal repeats (LTRs) at each end of genome regulate viral gene expression, viral integration into host genome and replication. The gag, env, pol sequences encode core structural proteins, viral envelop glycoproteins and viral enzymes respectively.

CD4 and chemokine co- receptors CCR5 or CXCR4 on host cell surface function as HIV-1 receptors.

gp120 protein on the surface of the virus binds to CD4 receptor on the host cell membrane, undergo conformational change which promotes secondary gp120 binding to chemokine co-receptor. This leads to conformational change in gp41 that exposes fusion peptide which inserts into cell membrane and enables viral membrane fuse with target cell membrane.

Viral envelope is removed by enzymes present in cell. Internal core is exposed and broken down. Viral RNA and enzymes enter into cytoplasm.

The HIV transcriptase make the single strand DNA copy of the viral RNA and subsequently double strand DNA is produced.

Viral DNA and integrase enter the nucleus. Viral integrase allows integration of viral DNA into t host chromosome as a provirus, provides the latency that enables the virus to evade the host responses so effectively.

Transcription of genes of integrated DNA provirus is regulated by the LTR upstream of viral structural genes and cytokines or other physiological stimuli to T cells and macrophages.

Initiation of HIV gene transcription in T cells is linked to activation T cells by an antigen or cytokines. This phenomena is important in pathogenesis of AIDS because end of latency and, virus production begins, infection of additional cells occur for stimuli from microbe.

Exported from nucleus and subsequent translation of mRNA leading to synthesis of viral