Cimetidine-induced augmentation of human lymphocyte blastogenesis by mitogen, bacterial antigen, and alloantigen

The effect of Cimetidine, a histamine-type 2 receptor antagonist, was evaluated on the in vitro proliferative response of normal human peripheral blood lymphocytes (PBLs). Cimetidine (10(-3) to 10(-8) M) increased mitogen-induced blastogenesis by 22% (phytohemagglutinin (PHA) and by 27% (pokeweed) over nondrug-treated control values (P less than 005 for PHA and pokeweed). Preincubation of PBLs with Cimetidine further augmented blastogenesis as much as 2- to 3-fold (P less than 0.005 for both mitogens). Multiple testing of the same normal subject demonstrated consistent reproducibility of increased proliferation by Cimetidine. Similar statistically significant amplifications of the proliferative res-ponse were observed when bacterial antigen (streptokinase-streptodornase) or alloantigen was used to induce blastogenesis. Optimally effective concentrations of Cimetidine ranged from 10(-5) to 10(-7) M, which corresponds to expected clinical serum levels. These observations suggest that a histamine-type 2 receptor antagonist is capable of modulating the proliferative response of PBLs in the absence of exogenously added histamine. The immunoregulatory implication of this Cimetidine-induced proliferative augmentation is discussed in relation to clinical transplantation and cancer immunotherapy.