Comparison of Mitomycin C and X-rays for the Production of One-way Stimulation in Mixed Leucocyte Cultures

IT has been suggested that the mixed leucocyte reaction is triggered by antigenic differences between the two leucocyte populations involving the chief histocompatibility systems in the rat 1,2 and in man 3 . Recent studies with mouse leucocytes indicate that antigens of the weaker H systems may also induce lymphocyte transformation in vitro 4 . For use as a histocompatibility test a unidirectional mixed leucocyte reaction is desirable. To produce cultures in which one-way stimulation occurs the lymphocytes of one partner must be capable of responding to an antigenic stimulus, while the cells from the second partner should be immunologically unreactive and yet stimulatory. This second population can be produced in a number of ways. ( a ) Freezing and thawing the stimulating cells will render them unresponsive, but such disrupted cells cause very weak reactions 5,6 . ( b ) Stimulating populations of macrophages can be produced from blood leucocytes by a short period of culture, before mixing with the allogeneic “responder” cells 7 . This method, however, is time consuming. ( c ) The stimulator cells can be rendered unresponsive by pre-treatment with mitomycin C 8,10 or by high doses of X-irradiation 9 . I have compared the effectiveness of the last two methods using the same samples of cells in cultures set up simultaneously.