Uptake by Mononuclear Phagocytes of Protein-Coated Bentonite Particles Stabilized with a Carbodiimide

The rate of phagocytosis and digestion of inert particles by cultured mononuclear phagocytes can be conveniently measured with bentonite particles which are readily coated with antigenically defined, iodine-125 labeled protein. Reaction of the protein coat with 1-ethyl,3-(3-dimethylaminopropyl) carbodiimide limits release of protein from particles in cell suspensions. The mechanism by which the carbodiimide stabilized the particle coat is not certain. Large mononuclear phagocytic cells developed within 7 days in cultures of guinea pig splenic leukocytes in isologous serum. These cells phagocytized protein-coated particles more slowly than did freshly isolated polymorphonuclear leukocytes. The per cent of particles phagocytized depended upon the nature of the particle coat. Particle uptake by cells cultured on a glass surface was difficult to demonstrate in the absence of opsonin. Uptake was stimulated by nonspecific heat-labile opsonins of normal serum and by specific, heat-stable opsonins of immune serum. Evidence is presented that isolated antibovine γ-globulin antibody obtained from an immune adsorbent, is such a specific opsonin. The nonspecific opsonins of normal serum shared several properties of the serum complement system. Within 60 min, 10-2 M sodium iodoacetate, sodium fluoride or sodium azide inhibited phagocytosis by cultured guinea pig mononuclear phagocytes.