NONSPECIFIC-BINDING BY MACROPHAGES - EXISTENCE OF DIFFERENT ADHESIVE MECHANISMS AND MODULATION BY METABOLIC-INHIBITORS

Abstract

Rat peritoneal cells were made to bind test particles of the following 5 different species: Ig-coated sheep red cells (IGSRC), glutaraldehyde-treated sheep red cells (GSRC), Leishmania, latex beads and tumor cells [rat methylcholanthrene-induced fibrosarcoma]. The dependence of binding on various physiochemical parameters was studied. The binding of latex or Leishmania resisted cold (4.degree. C), azide, cytochalasin B, ethyleneglycol and dimethylsulphoxide (DMSO). The binding of IGSRC resisted cold and azide; it was inhibited by cytochalasin B, ethyleneglycol and DMSO. The binding of GSRC was inhibited by cold, azide and ethyleneglycol, but not by cytochalasin B and DMSO. The binding of tumor cells was inhibited by azide, cytochalasin B, ethyleneglycol and DMSO. An attempt was made to saturate selectively some adhesive sites of macrophage membranes. Glutaraldehyde-treated bovine serum albumin (GBSA) inhibited the ingestion of latex and GSRC, not Leishmania and IGSRC; a crude Leishmania extract (CLE) inhibited the ingestion of all tested particles except latex. Antigen-antibody complexes inhibited the ingestion of IGSRC and Leishmania, not latex and GSRC. Rat macrophages were made to bind radio-iodinated GBSA (GIBSA). The uptake of glutaraldehyde-treated albumin was proportional to the amount of substrate the cells were incubated with over a wide concentration range. This uptake was not a result of endocytosis; it was far more efficient than that of peroxidase. Macrophage-particle interaction was studied with EM. The binding of IGSRC and Leishmania to macrophages involved large areas where the interacting membranes were separated by a low density gap of constant width. The interaction of GSRC and latex with macrophages was much more patchy and irregular. No redistribution of the macrophage surface polysaccharides seemed associated with the binding of GSRC. Several different mechanism and different membrane adhesive structures apparently are involved in non-specific recognition by macrophages. Non-specific binding sometimes requires an active cell participation. Several testable hypotheses are described, which suggest further experiments to obtain a fuller insight into the mechanism of rosette formation.