Increased Activity of Some Folic Acid Enzyme Systems in Infectious Mononucleosis

LTHOUGH infectious mononucleosis is a benign disease, many manifestations are similar to those observed in malignant transformation of lymphocytes. Among these are generalized lymphadenopathy and hepatosplenomegaly, the occurrence of morphologically abnormal cells in the periphera! blood and occasionally in the bone marrow, associated Coombs’ positive hemolytic anemias, and abnormal protein production. The peripheral blood cell of infectious mononucleosis is perhaps best characterized as an atypical large lymphocyte. These “atypical cells” have been shown by Bond et al.1 and Gavosto et al.2 to incorporate tritiated H thymidine in vitro to a considerably greater degree than do normal circulating leukocytes. An increase in the number of cells which label with H3 thymidine has likewise been seen in !eukocytes from patients with acute and chronic granulocytic leukemia, and in immature lymphocytes from certain patients with lymphatic leukemia.1 This finding indicates that infectious mononucleosis cells are actively synthesizing DNA and are comparable, in this regard, to those seen in leukemia. The present study was undertaken to make biochemical observations on these atypical lymphocytes and to contrast them with normal cells and leukemic cells. Three enzymes involved in folic acid metabolism, and thus important in cellular replication, were studied, as well as glucose-6-phosphate dehydrogenase.