Erythrocyte agglutination by wheat germ agglutinin: ionic strength dependence of the contact seam topology

The topology of the cell-cell contact seam formed when normal or pronase pr e-treated (PPT) erythrocytes are exposed to wheat germ agglutinin (WGA) in isotonic media of different ionic strengths was examined here. Lectin uptak e and cell agglutination were also quantified. Agglutination of normal cell s was gradually and significantly inhibited as ionic strength (IS) was redu ced from 0.15(buffered 145 mM NaCl) to 0.105. Agglutination was less inhibi ted in PPT cells, even when IS was reduced to 0.09. Cell contact seams form ed during agglutination showed patterns of localized contacts. The scale of the patterns, i.e, the average lateral separation distance of contact regi ons, was 0.62 mum for normal cells and was significantly shorter, at 0.44 m um, for PPT cells at an IS of 0.15. The scale increased significantly for b oth cell types when the IS was reduced to 0.09. Flow cytometry measurements showed that WGA uptake by normal cells increased slightly, whilst that for PPT cells was unchanged, as IS was decreased from 0.15 to 0.09. The result s imply that, whilst ionic strength change does not exert a strong influenc e on intermolecular WGA-ligand binding, physico-chemical modification of th e interaction between cells modulates not only the extent and progression o f the biospecific lectin-induced cell-cell agglutination but also the topol ogy of the contact seam. The IS dependence of contact separation in WGA-agg lutinated cells is contrasted here with that reported for cells adhering in dextran solutions. The influence of IS change and pronase pre-treatment on contact pattern are consistent with predictions, from interfacial instabil ity theory, of punctuate thinning of the aqueous layer separating bilayer m embranes in close apposition.