C1q binding to mitochondria: a possible artefact?

Mitochondrial preparations, obtained from human tonsils and from rat spleen, liver, heart, and kidney tissues, bound [125I]C1q with affinities of 10(7)-10(8)M-1. The binding of C1q was not affected by treatment of the mitochondrial preparations with pronase, trypsin, or phospholipase D, but it was lowered 5-6-fold following treatment of the mitochondria with DNase and RNase. Binding of C1q to mitochondrial preparations was also greatly diminished by limited chemical modification of C1q with cyclohexane-1,2-dione. It is suggested that the reported binding of C1q to mitochondria may have arisen from the protein binding to DNA and/or RNA contaminating the mitochondrial preparations.