Granulocyte chalone assayed in vivo in the mouse.

An in vivo system has been developed for estimating the inhibitory activities of granulocyte chalone which overcomes the objection to the use of mixed proliferating target cells. It depends on the identification of labelled mature granulocytes in the peripheral blood of mice that received a radioactive precursor of DNA synthesis, with and without granulocyte extracts, several days previously. Two extracts of bovine granulocytes were tested. The first demonstrated that maximum inhibition was achived when it was given 2 h before the isotope, suggesting that its activity was short lived. It also failed to depress the labelling index of peripheral lymphocytes, thereby demonstrating tissue specificity. The second was used to show that the dose-response relationship was exponential.