Is the macrophage the stimulating cell?

Using CAF1 spleen cells to stimulate parental strain BALB/c spleen cells in a mixed lymphocyte culture, column separation of responding cells increased their response whereas the same treatment of stimulating cells reduced their activity approximately 95 per cent. Peritoneal macrophages from CAF1 mice were found to stimulate BALB/c spleen cells poorly if present in comparable numbers or if they were cultured for 24 hours before adding responding cells. However, if the F1 macrophages were in contact with the BALB/c cells for only 4 hours, their stimulating effect was increased strikingly. Under these conditions BALB/c macrophages had no effect. It is concluded that the macrophage is probably the most effective stimulating cell and may be the only cell with this capability.