SURVEY OF RADIOACTIVE AGENTS FOR INVITRO LABELING OF PHAGOCYTIC LEUKOCYTES .2. PARTICLES

Abstract

When various radioactive particles were incubated and tumbled in concentrated suspensions of blood phagocytes [human] at body temperature for 1 h, they were bound to the phagocytic cells with a labeling yield of 30-40%. In vitro experiments showed that, for some radioactive colloids, a sizeable fraction of the total cellular binding resulted from nonspecific surface adsorption to other cells and from reversible surface adsorption to phagocytes without engulfment. No completely satisfactory in vitro methods was found for separating leukocytes with completely engulfed particles from those with surface-adherent particles; nonetheless, surface adherence can be partially reversed by 20% acid citrate dextrose (ACD) solution or by an excess of nonradioactive colloid. Gelatinization of colloidal particles tended to increase their binding to phagocytic cells but also increased the degree of nonspecific adherence to other cells. 99mte-millimicrospheres, 0.5-2 .mu.m in diameter, were optimal in size for phagocytosis by neutrophils and their nonspecific adherence to other cells was minimal. Because of the microspheres'' poor stability in aqueous suspension, it was technically difficult to separate free from phagocytosed radioactivity after cell incubation. The highly stable small-particle colloids (< 0.1 .mu.m), such as 198Au-colloid or 111In-colloid without Fe carrier, were phagocytosed poorly or not at all by neutrophils, although they were engulfed by mononuclear cells.