A 19-year-old man presents with fever, cervical lymphadenopathy, splenomegaly and atypical lymphocytosis. Amoxicillin given empirically was followed by a generalized morbilliform rash. The heterophile antibodies responsible for his positive Paul-Bunnell test are directed against:
- A Antigens on sheep red blood cells ✓
- B Viral gp350 envelope glycoprotein of the infecting virus
- C Smooth muscle and nuclear antigens
- D IgM Fc fragments bound to rheumatoid factor
Correct answer: A. Antigens on sheep red blood cells
Explanation
This is Epstein-Barr virus infectious mononucleosis. Heterophile antibodies are nonspecific IgM antibodies that agglutinate sheep and horse erythrocytes, forming the basis of the Paul-Bunnell and Monospot tests. The ampicillin/amoxicillin rash is a classical clue. CMV can cause a heterophile-negative mononucleosis syndrome, which kills that distractor, and EBV gp350 is the target of neutralizing antibody rather than heterophile antibody.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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