Roitt Immunology Mcq | 2026 Release |

A kidney transplant recipient develops acute cellular rejection on day 8 post-transplant. The predominant cells infiltrating the graft are:

C. C5a Explanation: Both C3a and C5a are anaphylatoxins, but C5a is far more potent in inducing mast cell degranulation and chemotaxis. Roitt questions often ask for "most potent" to discriminate between similar options. roitt immunology mcq

| Topic | Classic Clue in Question | Defect / Mechanism | |-------|--------------------------|---------------------| | XLA (Bruton’s) | Recurrent pyogenic infections after 6 months, absent tonsils | Btk mutation → arrest at pre‑B stage | | DiGeorge syndrome | Hypocalcaemia, congenital heart disease, absent thymus | 22q11 deletion → T‑cell deficiency | | CGD | Recurrent catalase‑positive bacteria (S. aureus, Aspergillus) | NADPH oxidase defect → negative NBT test | | Hereditary angioedema | Recurrent swelling without urticaria, normal C3/C4, low C1‑INH | C1 esterase inhibitor deficiency | | Type I hypersensitivity | Immediate wheal & flare, elevated IgE, mast cell tryptase | Cross‑linking of IgE on FcεRI | | SLE | ANA+, anti‑dsDNA, low C3/C4, “butterfly rash” | Type II (anti‑DNA) + Type III (immune complexes) | Roitt questions often ask for "most potent" to

A 2-month-old infant presents with persistent oral candidiasis, chronic diarrhea, and failure to thrive. Flow cytometry reveals absent T cells but normal B cells and NK cells. Which genetic defect is most likely? Flow cytometry reveals absent T cells but normal

: C) Dendritic cells