C4A and neoplasm: While our data demonstrates a lack of CDC activity in vivo (Additional file 3: Figure S3b) owing to a 2-base pair deletion in the complement C5 structural gene [53], it is possible that anti-CAIX deposition on the tumor cells can lead to activation of earlier complement components including C3a and C4a that can lead to chemotactic recruitment of myeloid cells and C3b to promote opsonization.