ROSETTE ASSAY FOR THE DETERMINATION OF C-1-Q RECEPTOR-BEARING CELLS

A rosette assay for identification of cells with receptors for C1q [fragment q of complement component I] was described. Glutaraldehyde-treated bovine erythrocytes bound C1q specifically, and the reagent thus prepared provided a valid indicator for rosette formation mediated by C1q receptors. Presence of these receptors on the membrane of a subset of human peripheral lymphocytes (mainly non-T [thymus-derived] cells) and on B[bone marrow]-derived lymphoblastoid cells was confirmed. Rosette formation was dependent on number of C1q molecules bound/indicator cell and was specifically inhibited by soluble native C1q and pepsin-resistant C1q fragments. These data, together with the reduced binding activity of C1r-C1s-associated C1q, indicated that C1q binding sites for lymphoid membranes were expressed on the collagen-like moiety, C1q rosette formation provided a simple new procedure for fractionation of human lymphocyte populations and separation from phagocytes that do not express receptors for C1q.