Using polymerized C9 to produce a monoclonal antibody against a neoantigen of the human terminal complement complex

The terminal complement complex (TCC), consisting of C5b, C6, C7, C8, and C9, contains neoantigens that are absent from the individual native components. Neoantigens are present both in the membrane-bound (MAC) and the fluid-phase (SC5b-9) complex. The present study describes production of monoclonal antibodies (MoAbs) against neoantigens of both forms of the TCC using human C9 polymerized in Zn2+ as an immunogen. One of ten MoAbs obtained, MoAb 1B4, reacted with the tubular C9 polymer, but not with either the native or sodium dodecyl sulfate-denatured monomeric C9, as shown by enzyme-linked immunosorbent assay and Western blotting. Moreover, MoAb 1B4 cross-reacted both with MAC and SC5b-9. This suggests MoAb 1B4 recognized a neoantigen in the moiety of C9 polymer in the TCC. MoAb 1B4 will be of value for definitive identification of MAC and for quantitation of SC5b-9 in plasma and urine.