Mouse bone marrow-derived mast cells and mast cell lines constitutively produce B cell growth and differentiation activities.

The present report describes a novel function of mast cells that consists of a B cell growth activity. The B cell response occurred without any stimulation or preactivation of mast cells. A small number of mast cells was required, since mast cell/B cell ratios as low as 1/100 to 1/10,000 lead to effective B cell activation. Mast cell-dependent B cell activation resulted, within 48 h of incubation, in blast formation, proliferation, and IgM production. Both low and high density B cells were responsive to mast cells. Supernatants from unstimulated mast cells could also activate B cells, suggesting that a B cell-stimulating activity (MC-BSA) is mediated by a soluble factor(s). The addition of anti-IL-4 or anti-IL-6 mAbs or even proteases to the mast cell-derived supernatants did not alter B cell activation. However, treatment of mast cells with mitomycin C or actinomycin D, or paraformaldehyde fixation totally abrogated MC-BSA. Fractionation of mast cell supernatant by gel filtration chromatography resulted in four peaks, ranging from > 200 to 15 kDa, all of which were biologically active on B cells. Because mast cells are known to continuously release proteoglycans, MC-BSA was subjected to chondroitinase and heparinase treatment, but no significant inhibition of B cell activation was obtained. This direct T cell-independent stimulatory effect of mast cells on B cells could account for a mechanism by which plasma cells are continuously produced in lymphoid organs and particularly in bone marrow.

Immobilized metal ion affinity partitioning of cells in aqueous two-phase systems: erythrocytes as a model.

Immobilized metal ion affinity partitioning of erythrocytes from different species is described. We have explored the affinity between transition metal chelates and metal-binding sites situated on the cell surface by partitioning in aqueous two-phase system composed of poly(ethylene glycol) and dextran. Soluble metal-chelate-poly(ethylene glycol) was prepared by fixing metal ions to poly(ethylene glycol) via the covalently bonded chelator, iminodiacetic acid. The partitioning behaviour of erythrocytes in systems at different concentrations of the ligand was tested. The copper-chelate-poly(ethylene glycol) was quite effective in the affinity extraction of human and rabbit erythrocytes, while the zinc-chelate-poly(ethylene glycol) displayed significant affinity only to the rabbit cells. Furthermore, the influence of various effectors such as imidazole, sialic acid on immobilized metal ion affinity partitioning of erythrocytes was examined.

Cell surface interactions with metal chelates.

We have explored immobilized metal ion affinity adsorption as a means of discrimination between cells and to assess partially the types of interaction that might contribute to the adsorption of cells on the such adsorbents. Erythrocytes from different sources were adsorbed on immobilized iminodiacetic acid charged with Cu2+, Ni2+ or Zn2+. The affinity of the human erythrocytes for the immobilized metal ions follows the order Cu2+ greater than Ni2+ greater than Zn2+. The adsorption capacity of the rat erythrocytes decreased in the following order: Zn2+ greater than Ni2+ greater than Cu2+. Pre-saturation of the columns with imidazole lead to the recovery of over 90% of the cells applied on the columns. Enzymic removal of sialic acid residues from the surface of erythrocytes has no effect on the adsorption-elution profiles of these cells on affinity adsorbents. These findings suggest that histidine residues localized on the cell surface are involved in the cell binding to the adsorbent. This new separation principle could be expanded to other types of cell. It could be used as a diagnostic tool and for separation, as well as for probing cell surfaces.