Influence of the spleen on the blood distribution of the leukocytes producing colony-stimulating activity (CSA) in man

The colony-stimulating activity (CSA) produced by the blood leukocytes has been studied before and after epinephrine administration in ten normal, 15 splenomegalic, and seven splenectomized subjects through a double layer agar culture system. A significant increase of mean values of the CSA per milliliter produced by blood monocytes has been observed after epinephrine administration in the groups of normal and of splenomegalic subjects. In the group of splenectomized subjects the baseline mean value of CSA per milliliter of blood was higher than those observed in the other groups, but it did not show any increase after epinephrine infusion. The CSA produced by 10⁶ blood leukocytes was similar in all three groups of subjects, and it was not similarly modified by epinephrine administration. Our results seem to indicate that the leukocytes producing CSA are distributed within two rapidly exchangeable blood compartments, the spleen representing an important section of the marginal compartment of blood monocytes.