Circulating atypical mononuclear cells, often unassociated with fever, splenomegaly, and lymphocytosis, have been observed in the postoperative period in patients who have had open heart surgery. Foster1 reported these findings in 30 of 180 patients at the Alfred Hospital in Melbourne. A related syndrome was also observed in two patients transfused with large volumes of blood, who were not subjected to cardiopulmonary bypass or cardiac surgery. The absence of neutrophilia, anemia, bacteremia, and elevated alkaline phosphatase values differentiated the posttransfusion mononucleosis associated with heart surgery or bypass from acute or subacute bacterial endocarditis. Furthermore, patients with posttransfusion mononucleosis did not display the usual features of infectious mononucleosis: pharyngitis, lymphadenopathy, and a positive Paul Bunnell test.
Electron microscopic study of the atypical cells confirms their identity as lymphocytes, which resemble lymphoblasts in tissue culture under the influence of phytohemagglutinin. The cells appear to have participated in immunological reactions. Tritiated thymidine