Phenylhydrazine is a mitogen and activator of lymphoid cells

Rats were administered a single injection of phenylhydrazine (PHZ) which induced an hemolytic anemia that reached maximal levels two to four days following injection. This was accompanied by a leukocytosis which was most pronounced four to six days after injection; lymphocytes and monocytes accounted for 75 percent to 80 percent of the leukocyte count, respectively. All peripheral blood cell values, including the red cell count and hematocrit, returned to their pre-injection levels by the 11th post-injection day. Analysis by flow cytometry of peripheral blood mononuclear cells (PBMC) isolated from PHZ-treated rats by Ficoll-Hypaque gradient separation showed a marked increase in the B cell population of the peripheral blood. This was also seen in cultures of PBMC obtained from untreated rats following incubation with PHZ. Cultures of PBMC obtained from rats four to five days after PHZ injection which were incubated with pokewood mitogen (PWM) or phytohemagglutinin (PHA) showed significant increases in blastogenesis as indicated by [3H] thymidine incorporation when compared to cultures of PBMC obtained from untreated rats incubated with these mitogens. Incubation of cultures of PBMC obtained from untreated rats with PHZ significantly increased blastogenesis in cultures of five day duration. Atypical and blastic lymphoid cells were evident in cytosmears of PBMC isolated from PHZ-treated rats and also in sections of PBMC pellets studied using the transmission electron microscope. Serum of the PHZ-treated rats contained elevated immunoglobulin titers as measured by radial immunodiffusion. The results show that PHZ stimulates lymphoid cell blastogenesis and can sensitize circulating lymphoid cells to PHA and PWM indicating that PHZ is capable of stimulating the immune system of the rat.