FATE OF MOUSE MACROPHAGES RADIOLABELED WITH PKH-95 AND INJECTED INTRAVENOUSLY

Mouse macrophages purified by elutriation from thioglycollate-induced peritoneal exudate cells were labelled with indium-111-oxine and injec ted intravenously into mice. A substantial amount of unbound radioacti vity remained in the circulation, suggesting that the radionuclide was not stably bound to the cells. Culture experiments with radiolabelled cells showed that indium-111 was released in the medium. Another cell marker, PKH-95, an iodine-125-labelled aliphatic compound insertable into the cell membrane, bound more stably than indium-111. Five minute s after injection of I-125-PKH-95-labelled macrophages, about 98% of t he cells were in a non-circulating pool. It was checked that PKH-95 la belling did not compromise the viability and functions of the macropha ges and that autologous erythrocytes and blood mononuclear cells label led with PKH-95 remained in the circulation after i.v. injection. One hour after injection, I-125-PKH-95-labelled macrophages were distribut ed mainly in lung (36%), liver (19%) and spleen (5%). Subsequently, ra dioactivity decreased in the lung while increasing in liver, spleen an d in an artificially induced footpad inflammation. The radioactivity a ccumulation in the inflammation persisted at least for 7 days. It repr esented a small proportion of radioactivity injected (0.2%) but was tr apped very specifically in the inflammation. This raised the hypothesi s that macrophages of the non-circulating pool could be released in th e circulation and recruited into the inflammation with slow kinetics.