Binding of histamine- and other ligand-conjugated macromolecules to lymphocytes

The presence of histamine receptors on lymphocyte membranes was investigated using conjugates of histamine and macromolecules tritiated or iodinated with I-125. Histamine-RSA conjugate binds to lymphocytes and causes patching and capping of the bound conjugate. It was found, however, that free histamine did not inhibit the binding of histamine-rabbit serum albumin to mouse lymphocytes, nor did His-RSA interfere with the binding of free histamine. In addition conjugates between RSA and other small molecules, such as ethylamine, ethanolamine, tyramine and glycine, were found to bind to the same sites on lymphocyte membrane as did His-RSA. Ethylamine-RSA like His-RSA when coupled to Sepharose, was capable of removing antibody producing cells from spleen cells of mice immunized against sheep red blood cells. In addition, when spleen cells from such immunized mice were passed through ethylamine or histamine-RSA-Sepharose and the unbound cells were subsequently injected into X-irradiated mice, a 1.8 fold increase in the immunological response was noted. We conclude that the selective binding to lymphocytes of the various ligand-macromolecular conjugates may be due to some general properties of the cell membrane and not to any specific receptors. Nevertheless, these conjugates can be used as a tool to remove selectively antibody producing cells as well as some regulatory cells.