Concanavalin A receptor sites on lymph node cells in vivo and in vitro

The distribution and density of receptors for concanavalin A (Con A) on the surfaces of cells of intact and isolated popliteal and axillary lymph nodes were investigated in the rabbit. Intact lymph nodes were perfused via the subcapsular (marginal) sinus with either Con A peroxidase or Con A ferritin, fixed with glutaraldehyde, and processed for electron microscopy. Both Con A peroxidase and Con A ferritin were distributed on the plasmalemma of lymphocytes, macrophages, neutrophils, plasma cells, reticular endothelial cells, and the vascular endothelium. Counts of Con A-conjugated ferritin particles indicated that the density of Con A receptors was generally similar for lymphocytes, macrophages, and neutrophils but lower on plasma cells. When lymph node cells were isolated by mechanical methods and exposed to Con A ferritin, the label was homogenously distributed on the cell surfaces of most cells. However, Con A binding was significantly higher on the surface of isolated cells than in the intact node. It is suggested that the increase in density of Con A binding sites on isolated cells may possibly be due to an unmasking of cell surface moieties in which additional Con A receptor sites become available as a result of the isolation procedure. The density of Con A ferritin binding sites was also significantly lower on the surface of isolated plasma cells than the lymphocyte and macrophage, suggesting that the density distribution of cell surface saccharides is different for various lymphoid cells.