Sugar receptors of the stromal cell layer in human long-term bone marrow cultures: their presence, modulatory responses to changes in the microenvironment and potential role in cellular adhesion.

Intimate cellular contacts and coordinated supply of regulatory factors are required to maintain the still inexplicable dynamic equilibrium of hemopoiesis. To infer the potential participation of protein-carbohydrate interaction in this complex process, human long-term bone marrow cultures were initiated from eleven donors, and the adherent cell layer was characterized enzyme- and immunohistochemically. Utilizing an array of carrier-immobilized carbohydrate ligands and sulfated polysaccharides as probes, specific binding of various constituents of the carbohydrate chains of cellular glycoconjugates to the stromal cells was unmistakably disclosed. Biochemical analysis, employing glycocytologically effective ligands in affinity chromatography, corroborated this result. The extent of binding was markedly lower in the two samples, derived from leukemia patients. Pronounced adaptive responses for this characteristic followed changes in the culture microenvironment that are known to influence qualitative and quantitative aspects of hemopoiesis in vitro, namely omission of hydrocortisone and horse serum or addition of cytokines. Similarly, such adaptive modulation occurred on the level of accessible cell surface receptors, monitored by neoglycoenzymes. These binding sites can be involved in mediation of cellular interactions, as revealed in a model system by the interference of N-acetyl-D-galactosamine in cell adhesion. Overall, the results support the idea that glycobiological recognition may contribute to the functional integrity of the stromal cell layer as well as provide the basis for further analysis.