Enhancing effects of IL-2 on M-CSF production by human peripheral blood monocytes

Monocytes have the capacity to produce granulopoietic factors such as M-CSF and G-CSF. Our findings here showed that interleukin-2 (IL-2), at a concentration of more than 0.05 ng/ml, led to a 12-fold increase in the production of M-CSF in the human peripheral blood mononuclear cells after 72 h incubation compared to the control culture. Even in purified monocyte cultures with added IL-2, a 3-fold increase in M-CSF production was observed at an IL-2 concentration of 50 ng/ml. The enhancing effect of IL-2 on M-CSF secretion was also observed when IL-2-stimulated non-phagocytic cell-conditioned medium was added to monocyte cultures. These results indicated that IL-2, both directly and indirectly, activated monocytes to enhance the production of M-CSF. In addition, the expression of IL-2 receptor (CD25) on monocytes was more enhanced in cultures containing IL-2 than in cultures without IL-2. On the other hand, IL-2 did not induce G-CSF production in purified monocytes. These in vitro results suggest that when IL-2 is used clinically, the various biological activities of M-CSF should also be taken into consideration.