Peripheral blood lymphocyte apoptosis: a clue to the diagnosis of acute infectious mononucleosis.

OBJECTIVE

To describe the morphology and significance of apoptotic lymphocytes in peripheral blood smears of patients with acute infectious mononucleosis. To our knowledge this has not been previously reported.

DESIGN

Peripheral blood smears from 27 patients with a positive heterophile antibody test were collected and reviewed for the presence of apoptotic lymphocytes. Flow cytometry was performed on three cases to document the previously described low expression of bcl-2 in lymphocytes in infectious mononucleosis. Four control patient populations comprising 80 cases were similarly screened for the presence of apoptotic lymphocytes.

SETTING

The specimens were collected over a 3-month period in two laboratories at our tertiary care hospital; all specimens were processed according to a standard protocol.

PATIENTS: Young adult military recruits and their spouses, military dependent adolescents, and retired military personnel.

RESULTS

Twenty-four (88.9%) of 27 peripheral blood smears of patients with acute infectious mononucleosis contained readily identifiable apoptotic lymphocytes. Three (3.75%) of 80 control peripheral blood smears were identified with rare apoptotic lymphocytes, all occurring in patients with viral upper respiratory infections.

CONCLUSIONS

The finding of apoptotic lymphocytes in a peripheral blood smear is useful in the differential diagnosis of infectious mononucleosis and neoplastic hematolymphoid processes.