The pattern of sugar inhibition of rosette formation, a model for intercellular interaction between cultured cells and glutaraldehyde-fixed, trypsinated rabbit erythrocytes, served to infer the presence of carbohydrate-binding proteins. This profile from cell extracts for the two murine macrophage-like cell lines, P388D1 and J774A.1, was comparatively analyzed by affinity chromatography on supports with immobilized carbohydrates (lactose, L-fucose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and maltose) or with the immobilized mannose-rich yeast glycoprotein mannan or fetuin-derived glycopeptides containing sialic acid residues. After elution with specific sugar in the absence of Ca2+ ions, the proteins were separated by sodium dodecyl sulfate – polyacrylamide slab gel electrophoresis. The composition of carbohydrate-binding proteins of the two lines clearly exhibited quantitative and qualitative differences. Moreover, the pattern of P388D1 cells was also demonstrated to change significantly in response to alterations in the conditions of the physiological environment. These alterations were imposed by in vitro growth, by subsequent in vivo growth in nude mice, and by re-adaptation of cells to culture after in vivo passage. Collectively, our observations and other physiological and biochemical reports on macrophage lectins indicate that the presence of sugar receptors with different specificities may be an indicator of macrophage differentiation, being reversibly modulated to a considerable extent by external factors, e.g., microenvironment. Extensive but selective alterations in this respect could play an important role in the control of recognition and effector mechanisms within diverse functions of macrophage subpopulations.
Endogenous lectins from cultured cells. Isolation and characterization of carbohydrate-binding proteins from 3T3 fibroblasts.
