Effect of putrescine and all-trans retinoic acid (ATRA) on immature dendritic cell (DC) phenotype. Cells were collected after immature DC preparation procedure (imm DC; n = 11) and treated with 10 mmol/l putrescine (Put; n = 10). To putrescine-treated DCs was added 1 μmol/l ATRA (Put + ATRA; n = 5). Data are expressed as percentage of cells (with standard error) expressing the HLA-DR+Lin- and HLA-DR-Lin- phenotypes. *P < 0.01 versus imm DCs; **P < 0.02 versus putrescine-treated imm DCs.