Evaluation of indium-111-2-mercaptopyridine-N-oxide for labeling leukocytes in plasma: a kit preparation.

Pure neutrophils, lymphocytes, and mixed leukocytes have been labeled in vitro with 111ln chelated to a nontoxic, water soluble agent 2-mercaptopyridine-N-oxide (Merc). Cells were labeled in isotonic salt-balanced medium with preformed [111ln] Merc (yield greater than 95%), or in 0.5 ml autologous plasma by incubation with dry Merc first and then with 111ln (yield 75%). The latter method facilitated a kit procedure that required 2 micrograms dry Merc when acid citrate dextrose was used as anticoagulant or 20 micrograms when heparin was used. Labeling efficiency was dependent on cell concentration and pH. Labeled cells accumulated avidly in experimental abscesses and provided abscess/blood ratios of greater than 75 at 24 hr postinjection. In dogs, the liver uptake of labeled cells was only 18.8 +/- 7.1% compared to that of 48.5% when cells were labeled with [111ln]oxine.