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Solution


Q.

HIV that causes AIDS, first starts destroying                       [2015]
1 helper T-lymphocytes  
2 thrombocytes  
3 B-lymphocytes  
4 leucocytes  

Ans.

(1)

The AIDS retrovirus, called human immunodeficiency virus (HIV), mounts a direct attack on CD4+ T helper cells because it recognizes the CD4 coreceptors associated with these cells.
HIV attack on CD4+ T cells cripples the immune system in at least three ways. First, HIV-infected cells die only after releasing replicated viruses that infect other CD4+ T cells, until the entire population of CD4+ T cells is destroyed. Second, HIV causes infected CD4+ T cells to secrete a soluble suppressing factor that blocks other T cells from responding to the HIV antigen. Finally, HIV may block transcription of MHC genes, hindering the recognition and destruction of infected CD4+ T cells, and thus protecting those cells from any remaining vestiges of the immune system. The combined effect of these responses to HIV infection is to wipe out the human immune defense.