Selective diphenylhydantoin-induced suppression of lymphocyte reactivity in vitro

Diphenylhydantoin (DPH) in concentrations approximating therapeutic blood levels was found to inhibit mixed lymphocyte culture (MLC) proliferation as measured by uptake of 3H-thymidine when compared to alkaline diluent required to solubilize the DPH. Control cultures containing diluent alone manifested inhibition of 3H-thymidine uptake relative to non-diluent-containing cultures. Both reactor and stimulator cells were independently capable of effecting this inhibition after treatment with DPH. An inconsistent effect of DPH on lymphocyte reactivity to graded doses of phytohemagglutinin and to pokeweed mitogen was observed. A possible association between the effect of DPH on MLC reactivity and the phenomenon of dilantin-induced lymphadenopathy is suggested.