Purification of fH and fH/CFHR3. Monoclonal antibodies specific for fH-402Tyr or fH-402His were coupled to HiTrap affinity columns and used to separate the allelic fH variants from a heterozygote control or the carrier IV:6 (the latter carried the mutated protein on the CFH402Y allele). The purified protein was eluted from the column, concentrated, and subjected to size exclusion on a Supedex 200 column (supplemental Figure 2). The purified proteins were analyzed by SDS-PAGE (A) and by Western blot with allele-specific monoclonal antibodies (B). This Western blot confirms that the mutant protein is encoded on the fH-402Tyr allele and illustrates that there is no cross-contamination of the protein preparations.