Immune recognition of molecules belonging to self is important to

Correct Answer: B

Rationale: Identification of self tells the immune system that the cell or molecule recognized is not a foe. Natural killer cells use this mechanism of self-recognition to halt their attack on cells that they perceive to be abnormal. Receptor generation by B and T cells occurs independently of initial encounter with self molecules. Pattern recognition receptors, on the other hand, are genetically programmed to recognize nonself. By triggering an attack on a cell expressing the self molecule, an immune recognition molecule violates its 'nonaggression pact' with the cells and molecules of the host and establishes an internal coup known as autoimmunity.

Correct Answer: C

Rationale: Neutrophils are the most abundant leukocytes (~50-70%) in blood, key for bacterial defense.

Correct Answer: B

Rationale: Somatic rearrangement and mutation generate diversity; not millions of genes or antigen shifting .

Correct Answer: A

Rationale: MHC I presents proteasome-derived peptides; phagolysosomes are MHC II.

Correct Answer: C

Rationale: The thoracic duct drains lymph into the left subclavian vein, returning it to the bloodstream.