The Mitotic Activity of Circulating Atypical Mononuclear Cells in Infectious Mononucleosis

An investigation has been made into the mitotic and premitotic activity ofthe circulating atypical mononuclear cells which occur in infectious mononucleosis. Dividing and binucleate cells were found in 2.4 per cent of blood filmsand in 63.9 per cent of white cell concentrates. The number of cells in mitosiswas small and they were most commonly encountered during the first threeweeks of the disease; cells in prophase and metaphase predominated. The incidence of dividing cells in white cell concentrates was increased by a preliminary period of incubation with colchicine. The uptake of ³H-thymidine wasshown to be increased during the first four weeks of the disease, with peaklabeling in the second and third weeks; in one autoradiograph, 5.4 per centlabeling was observed. The label was confined to the nuclei of certain atypicalmononuclear cells, most of which showed rather marked cytoplasmic basophilia. Karyotype analyses were consistently normal. The occurrence of similarlarge mononuclear cells, capable of taking up ³H-thymidine, in other pathological conditions and in normal subjects is stressed. Their origin, function andpotentialities are ill-understood at the present time.

Two further autoradiographic studies^21,22 dealing with the mitotic activityof atypical mononuclear cells in infectious mononucleosis have recently appeared, both of which record increased DNA synthesis. Epstein and Brecher²¹observed peak labeling during the first two weeks of the disease; most of thelabeled cells showed enhanced cytoplasmic basophilia. No variation in labeling at different phases of the disease was found by Schmid et al.,²² who,unlike previous workers, characterize the labeled cells in some detail asplasmacytoid, monocytoid and lymphocytoid elements.

Submitted on December 2, 1964 Accepted on February 14, 1965