A hapten Is...?

Correct Answer: C

Rationale: A hapten is a small molecule that can bind to antibodies but cannot induce an immune response unless attached to a carrier protein.

Correct Answer: D

Rationale: B cells exhibit allelic exclusion, but the expression of maternal or paternal alleles varies between individuals, though typically only one allele is expressed per B cell.

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.