A simple method for the determination of complement receptor-bearing mononuclear cells.

A simple method is described for the identification of mononuclear cells bearing the complement receptor. Gram-negative bacteria are directly fluoresceinated and then incubated in non-immune human serum, which leads to complement fixation via activation of the alternative complement pathway. Complement receptor-bearing mononuclear cells (CRMC) will form easily readable rosettes with these bacteria. The method requires no antibody preparation or purification, uses human serum rather than purified complement components or mouse serum, and gives results that correlate closely (r = 0.9015) with the EAC method of identifying CRMC. Furthermore, these indicator cells cannot bind to mononuclear cells via the E or IgG Fc receptors, eliminating this source of possible error. This method may be used for the identification of CRMC in suspension or frozen tissue sections.