Hyperacute graft rejection is caused by?

Correct Answer: A

Rationale: Hyperacute rejection is mediated by preformed antibodies that bind donor antigens, triggering immediate graft damage.

Correct Answer: D

Rationale: Gamma interferon (IFN-γ) from Th1 cells activates macrophages, enhancing phagocytosis, making it the most accurate statement.

Correct Answer: B

Rationale: C3 deficiency severely impairs opsonization, leading to recurrent infections with encapsulated bacteria like pneumococcus. Terminal complement deficiencies (C5-9) predispose to neisserial infections, while C1q and C1 inhibitor deficiencies have other manifestations.

Correct Answer: C

Rationale: Nezelof syndrome, a T-cell deficiency, can include skeletal anomalies like rib cage defects, though less commonly emphasized than in other conditions.

Correct Answer: D

Rationale: In DiGeorge syndrome, absolute lymphocyte counts vary; in partial forms, they may be normal or only mildly reduced, not always markedly low, making D untrue.