I isolate lymphocytes from leukapheresis filters. I try to proliferate the lymphocytes with PHA-P, but after MTT Assay the control is the same or higher. I use 100.000 cells in a 96wells plate and 5μg/ml PHA. The MTT is performed the third day of incubation (10 μl Mtt/well). I incubate 4 hours with mtt, centrifuge the cells, because they are not adherent and I dissolve the precipitate with 200μl of DMSO. After 15min I read the plate in Elisa reader. Any suggestions?