Reversible binding of sialidase-treated rat lymphocytes by homologous peritoneal macrophages.

After sialidase treatment, lymphocytes disappear from the blood stream, but reappear after a few hours. The behavior of sialidase-treated rat lymphocytes was investigated by in vitro binding studies with homologous peritoneal macrophages. A lymphocyte mixture from thymus and spleen was treated with sialidase and cultured up to 55 h, and at various times, the binding of the lymphocytes to glass-adherent macrophages was studied by light and electron microscopy; vital lymphocytes were only bound but not phagocytosed, and the interaction with macrophages was inhibited by D-galactose. During culture of lymphocytes, either separately or with macrophages, the binding was more and more reduced, and a second sialidase treatment of cultured lymphocytes led again to increased binding which could be inhibited by D-galactose. This change did not occur in the presence of N-acetyl-2,3-didehydro-2-deoxyneuraminic acid, an inhibitor of sialidases, showing the sialic acid specificity of this phenomenon. Thus, the reversibility of lymphocyte binding could be explained by resynthesis of cell surface sialic acids.