A 19-year-old man has five days of fever, exudative tonsillitis, and posterior cervical lymphadenopathy. The spleen tip is palpable. Peripheral smear shows 22% atypical lymphocytes and the heterophile antibody test is positive. The atypical lymphocytes seen in this condition are:

• A EBV-transformed B lymphocytes expressing CD21
• B Plasma cells secreting IgM heterophile antibody
• C Immature myeloid precursors released from the marrow
• D Activated CD8-positive cytotoxic T cells reacting against EBV-infected B cells ✓

Explanation

The striking atypical lymphocytosis of infectious mononucleosis represents a polyclonal expansion of activated CD8+ cytotoxic T cells responding to EBV-infected D cells, not the infected D cells themselves. Although EBV transforms D cells via CD21, those D cells are few in number in blood. The heterophile antibody comes from infected D cells, but plasma cells are not the circulating atypical forms seen on smear.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.