Inhibition of lymphocyte growth by Ulex seed extracts (USE)

Extracts produced from the seeds of Ulex europeus (European gorse) were found to contain an inhibitor of human and murine lymphocyte growth. Interference with lymphocyte growth was demonstrated in three test systems. (1) Ulex seed extracts (USE) prevented the uptake of tritiated thymidine by stimulated human T and B lymphocytes. (2) The numbers of sensitized murine lymphocytes releasing antibody were diminished after incubation with USE. (3) Murine lymphoid tumour cells cultured in the presence of USE had a reduced growth potential. Growth inhibition occurred independently of the mode of lymphocyte stimulation. Increased metabolic activity induced by plant seed mitogens, alloantigens and direct immunization, as well as that endogenously present in rapidly growing tumour cells, was similarly restricted. The inhibition of lymphocyte growth was not the result of cytotoxicity and was easily reversible by washing lymphocytes free of USE. The USE growth inhibitor was found not to be anti-H and appeared to function as an antithesis of stimulators found in other plant seed extracts.