In vitro proliferation of macrophage depleted human peripheral blood lymphocytes

The incorporation of thymidine by normal human peripheral blood lymphocytes was tested in vitro following various culture conditions. A significant increase of thymidine uptake was observed in cultures depleted of plastic adherent, nylon wook adherent, or phagocytic cells. This proliferative activity occurred in the presence of various sera but was not due to a blastogenic response to a foreign protein, since it was also observed when autologous plasma was the only source of protein in the culture medium. The similarities and differences between this 'spontaneous' proliferative phenomenon and other blastogenic responses which are regulated by macrophages are discussed.