Folate requirement for blast cell transformation in mixed leukocyte cultures.

Mixed leukocyte cultures from normal donors were set up in standard tissue culture media. Blast cell transformation was measured 6 days later by ³H-thymidine uptake and assessed qualitatively with stained smears. Media RPMI 1629 and RPMI 1640 allowed much more intense blastogenesis than Medium 199, the difference being due to the low folic acid content of Medium 199 (0.01 mg/liter) compared with RPMI 1629 (10 mg/liter) and RPMI 1640 (1 mg/liter). Further experiments indicated that folic acid increased the multiplication rate of blast cells but did not promote the induction or initial transformation phases of the mixed leukocyte reaction. The effect of folic acid on the PHA response was entirely different: ³H-thymidine uptake in 3 day PHA cultures was decreased, and there was no apparent effect on the number or percentage of blast cells seen on the smears. The reason for this difference is at present unknown, but some possibilities are discussed.