38.1 Acquired immunodeficiencies

Acquired immunodeficiencies are the ones that are not inherited but are acquired during lifetime. These may occur either as a biological complication of another disease or the diseases that develop due to complications of therapies for other diseases. Malnutrition, neoplasms, and infections are some of the conditions in which immunodeficiency acts as a complicating element. Other form of acquired immunodeficiency occurs in patients where spleen is absent or has been removed surgically.

38.1.1 HIV/AIDS

It is caused by human immunodeficiency virus (HIV) infection and is associated with opportunistic infections, malignant tumors and immunosuppression. It affects the immune system by killing dendritic cells, CD4+ helper T cells, and macrophages.

38.1.2 HIV structure and genes

HIV is a lentivirus belonging to the family Retroviridae . It infects macrophages, dendritic cells and CD4 T cells leading to immunosuppression. The structure of HIV virion consists of two copies of positive single stranded RNA, viral proteins and phospholipids. The size of RNA genome is 9.2kb in length with 3 important genes in addition to others. These three genes namely gag, pol, and env have specific roles to play in the pathogenicity of HIV. Gag encodes structural proteins, env encodes envelope glycoproteins gp120 and gp41 for infection, and pol encodes reverse transcriptase, integrase and viral protease enzymes needed for virus replication.

38.1.3 Viral life cycle

HIV gets transmitted from one person to the other through three possible ways.

1.  Sexual contact

2.  Blood transfusion or through milk

3.  Transplacental passage

 

CXCR4 and CCR5 are the chemokine receptors that act as co-receptors for HIV. CD4+ T-cells are the cells of choice for HIV replication. Once inside the cell, HIV exists in a provirus form after integration of viral DNA with the host cell genome. Long terminal repeats control the transcription of the provirus and full length viral transcripts are produced and expressed as proteins followed by the formation of an infectious virion.