The two groups of complement C3 proteins can be purified by GTX02807 C3 antibody [M68] immunoaffinity chromatography from the partially purified milk fractions. Human milk proteins were loaded onto CM-Sepharose 4B column and proteins, including C3, were eluted by different salt (NaCl) concentration. The slat concentration was smaller than 0.3 N. The CM low salt fractions were collected and loaded to the mAb M68-Sepharose column to purify C3. After washing the immunoaffinity column, the captured proteins were eluted by 0.1 N glycine buffer pH 2.4. The eluates were collected into several fractions, E1, E2, E3, E4, E5 and E6. E1-E4 fractions were analyzed by SDS-PAGE and the eluted proteins were stained by CBB. The protein band 2 and 7 as indicated are sliced out and subjected to MS/MS protein identification (by Prottech Inc.), confirming these bands to be complement C3. The relative abundance of peptides matching to C3 is 98% for band 2 and 96% for band 7. For the best detection sensitivity, the samples should be treated under non-boiled and non-reducing conditions. Lane A : Input (partially purified milk fractions) Lane B : Flow through Lane C : Elution 1 Lane D : Elution 2 Lane E : Elution 3 Lane F : Elution 4 Loading : 20 microl