CD8A and infectious mononucleosis: We now know that the characteristic atypical lymphocytes, carefully described morphologically by Downey and McKinlay,2 are actually activated CD8+ T cells,3 which are responding to EBV-infected B cells.4 Infectious mononucleosis represents a significant health risk because of the severity and duration of the acute illness and also because of the potential for long-term complications in the form of certain cancers and autoimmune diseases.