A simple method for preparation of C3c fragment from trypsinized serum‐ reacted zymosan

: A simple method for preparing relatively pure C3c fragment from serum-reacted zymosan is described. Although hyperimmunization studies indicate contamination of the "C3c" product by C3d and immunoglobulin antigenic materials, these are present in such small amounts that they do not impair the effectiveness of the product as a reagent for absorbing anti-C3c reactivity from polyspecific antisera. Furthermore, two of the three hyperimmune sera contained such weak anti-C3d that they could serve as monospecific anti-C3c antiglobulin reagents if used at moderate dilution. Neutralization of accompanying anti-IgG and weak anti-IgM is easily accomplished with readily available purified immunoglobulins. Preliminary studies indicate that the C3c product should be adaptable to quantitative radioimmunoassay of anti-C3c antibody concentrations and equilibrium constants.