The relationship of infection and DNA-synthesizing cells in human blood

An increase in DNA-synthesizing mononuclear cells in human blood during viral infection has been documented with the radioisotope tritiated thymidine (H 3 TDR). In this study, young men with either an induced bacterial (tularemia) or rickettsial (Q fever) disease were studied for a similar increase in such proliferative cells. Proliferative mononuclear cells were detected by incubating blood with H 3 TDR and the per cent labeled cells (labeling index) determined by radioautography. A definite, and in some cases striking, increase in the labeling index was always noted in association with clinical disease. A significant increase in H 3 TDR-labeled cells was noted when the subjects were febrile, but this increase was even more marked shortly after acute infection. However, 2 subjects exposed to Q fever developed significantly increased labeling indices with no evidence of clinical illness. Associated antibody studies disclosed no relationship between the changes in labeling index and the circulating antibody titer. Various mechanisms are considered to explain these findings, and it is felt the most likely explanation is that such proliferative cells are involved in inflammation and secondary reparative processes.