These atypical lymphocytes, aka Downey cells (Downey 1923), are actually activated CD8 T lymphocytes, most of which are responding to EBV-infected cells.

CD8+ T- cells increase in numbers in the blood stream and are activated (aka Downey cells, reactive lymphocytes or atypical lymphocytes because of their atypical presence in peripheral blood) to eliminate EBV infected B- lymphocytes.

FA 2017: Infects B cells through CD21. Atypical lymphocytes on peripheral blood smear G —not infected B cells but reactive cytotoxic T cells. ⊕ Monospot test—heterophile antibodies detected by agglutination of sheep or horse RBCs. Use of amoxicillin in mononucleosis can cause characteristic maculopapular rash.