Transfer of antigenic macromolecules from macrophages to lymphocytes. I. Autoradiographic and quantitative study of ( 14 C)endotoxin and ( 125 I)haemocyanin transfer.

Abstract

In an in vitro autologous system, studies were carried out on the transfer of either biosynthetically-labelled [(14)C]Salmonella enteritidis endotoxin or [(125)I]Maia squinado haemocyanin from macrophages to lymphocytes. When cultured 1 hour in vitro, lymphocytes adhered to autologous macrophages, forming lymphocyte-macrophage islands (LMI). Quantitative data obtained from stained thick sections showed that 1.8 per cent of the lymphocytes had adhered to macrophages with ingested [(14)C]endotoxin while 0.6 per cent of the lymphocytes adhered to macrophages with ingested [(125)I]haemocyanin. The presence of antigen macromolecules was observed mainly within lymphocytes adhering to macrophages with ingested antigens, i.e. at the level of LMI. On the other hand, autoradiography carried out on the same thick sections, showed that 0.20 per cent of the lymphocyte population in LMI possess silver grains. High resolution autoradiographic pictures of thin sections, showed a peculiar localization of silver grains in LMI lymphocytes: about 80 per cent of the radioactivity was found within lymphocytic nuclei and the remainder either on the cellular membrane or free in the cytoplasm. The disappearance of radioactivity from the LMI-located macrophage membranes (where lymphocytes contain silver grains) as well as the regular inhibition of antigen transfer occurring after pronase treatment of the macrophage which contained ingested antigen, strongly suggest that antigen bound to macrophage membrane was transferred to lymphocytes. As pretreatment of lymphocytes with anti-Ig serum resulted in regular inhibition of antigen transfer, it appears that the Ig receptors of lymphocyte membranes play an important role in the transfer mechanism. Combined technique, i.e. autoradiography and the peroxidase method for revealing Ig bound to lymphocyte membranes, showed that silver grains occurred only within lymphocytes displaying peroxidase-positive membrane.