Polymer microbeads bound to C3 fragments for detecting and labeling cells with C3 receptors

Monodisperse microbeads (mbs) of a hydrophilic polymer with diameters of 4 microns and 0.2 micron were prepared. To these mbs, IgM or a sugar was bound covalently, and then the mbs were treated with fresh human or mouse serum. This led to the activation of complement and to the binding of C3 fragments to the mbs. C3 fragments fixed on mbs varied with the type of immobilized substance on the mbs and the incubation time of the mbs with fresh serum. Three kinds of mbs binding C3 fragments were prepared: mbs binding C3b, C3bi and C3d (C3hu-mbs); the ones binding C3bi and C3d (C3mu-mbs); and the ones binding only C3b (C3bhu-mbs). They formed rosettes with cells which had the corresponding receptor. When lymphocytes were incubated with C3hu- or C3bhu-mbs with a diameter of 0.2 micron, cap formation of each receptor was observed under a microscope. Once prepared, C3hu-, C3mu- and C3bhu-mbs were stable for more than 4 months.