Demonstration of complement receptors on lymphoblastoid cells by radiolabeled antibodies and in situ autoradiography

Exposure of established human lymphoid lines to fresh human complement, followed by radiolabeled anti-C3 antibody and subsequent counting of radioactivity or autoradiography gave strong membrane-associated reactions with some lines but not with others. There was a good correspondence between complement membrane fluorescence (CMF) staining and the autoradiographic reaction. In all probability, these reactions detect a combination of alternate pathway activation and binding of the activated complement products to preformed complement receptors, but the autoradiographic reaction appears to be more sensitive. It also permits the localization and quantitation of the receptors on single cells. Raji cells were found to express the reactive receptor in 95% of the cells, with a high surface density. Daudi and Ramos contained 66 and 45% reactive cells, respectively. The receptor density was considerably lower than on Raji cells, in agreement with previous EAC-rosette tests. P3HR-1 cells that were negative for C3 receptors by both EAC rosetting and complement membrane fluorescence showed only trace reactivity in the autoradiographic test in a low percentage of the cells. Trypsin treatment, known to remove complement receptors without affecting alternate pathway activation, reduced or abolished the autoradiographic reaction.