A serum sample from a nontransfused male containing anti-Rh27 and an additional weakly reacting antibody was investigated. One absorption of the serum with R(Z)R(1) cells left only anti-Rh27 while repeated absorption with R(1)R(1) cells or autologous cells had no effect. Treatment of the serum with reducing agents destroyed all activity suggesting the antibody was predominantly IgM. Tests with monospecific antiglobulin reagents in the indirect antiglobulin test revealed very weak reactions with anti-IgM and anti-IgA, no reactions with anti-IgG, and strong reactions with anti-C3(C3c + C3d) and anti-C4. This is the first reported example of a naturally occurring complement binding anti-Rh27.

A serum sample from a nontransfused male containing anti-Rh27 and an additional weakly reacting antibody was investigated. One absorption of the serum with RZR1 cells left only anti-Rh27 while repeated absorption with R1R1 cells or autologous cells had no effect. Treatment of the serum with reducing agents destroyed all activity suggesting the antibody was predominantly IgM. Tests with monospecific antiglobulin reagents in the indirect antiglobulin test revealed very weak reactions with anti-IgM and anti-IgA, no reactions with anti-IgG, and strong reactions with anti-C3(C3c + C3d) and anti-C4. This is the first reported example of a naturally occurring complement binding anti-Rh27.