IMMUNO- DEFICIENCY DISEASES

Immuno-deficiency diseases result due to defect in one or more components of the innate or adaptive immunity . 

Affected individuals are suspectible to diseases which normally would not bother most people .  

Severe combined immuno-deficiency results du to one of many genetic defects . 

One of such genetic defects leads to adenosine deaminase deficiency  .

SCID is characterised  by a very low number of circulatory lymphocytes . 

The affected individuals usually die at an early age .

AIDS is an example of immuno-deficiency caused by the infection from a retrovirus known as Human immuno-deficiency virus .

 Retroviruses have RNA genomes that replicate via DNA intermediate .

HIV selectively infects and kill T-halper cells . The depletion in T-helper cells weakens the acquired immuno response and may abolish it completely .

The viral RNA genome is converted to DNA copy by the action of viral enzyme reverse transcriptase .

The DNA copy of  HIV becomes inserted into the human chromosome and replicates with the cellular DNA  .

It may also be transcribed to produce RNA copies of viral genome .

The RNA copies are packed and liberated as viral particle .

The infected cell is lysed in this process and the released virus particles infect new T-helper cells .