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STD 12 - 7. human health and disease — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYSTD 12 - 7. human health and disease1 Mark
MCQ
$HIV$ that causes $AIDS$, first starts destroying
  • ✓
    helper T­lymphocytes
  • B
    thrombocytes
  • C
    $B$-­lymphocytes
  • D
    leucocytes.
✓

Answer

Correct option: A.
helper T­lymphocytes
a
(a) : 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. $HIV’s$ attack on $CD4^+\ T$ cells cripples the immune system in at least three ways. First, HIV­infected cells die only after releasing replicated viruses that infect other $CD4^+\ T$ cells, until the entire population of $CD4^+\ T$ cell 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.

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