A rosette assay for the determination of C 1 q receptor-bearing cells

Abstract

A rosette assay for the identification of cells with receptors for C 1q is described. Glutaraldehyde‐treated bovine erythrocytes bound C 1q specifically, and the reagent thus prepared provided a valid indicator for rosette formation mediated by C 1 q receptors. The presence of these receptors on the membrane of a subset of human peripheral lymphocytes (mainly non‐T cells) and on B‐derived lymphoblastoid cells was confirmed. Rosette formation was dependent on the number of C 1 q molecules bound per indicator cell and was specifically inhibited by soluble native C 1 q and pepsin‐resistant C 1 q fragments. These data, together with the reduced binding activity of C 1r‐C 1s‐associated C 1q, indicated that the C 1 q binding sites for lymphoid membranes are expressed on the collagen‐like moiety, C 1q rosette formation provided a simple new procedure for fractionation of human lymphocyte populations and separation from phagocytes that do not express receptors for C 1 q.