New data on C1qDC from the colonial ascidian Botryllus schlosseri

In the compound ascidian Botryllus schlosseri, we recently identified a novel C1q-domain-containing (C1qDC) protein expressed by circulating immunocytes, called BsC1qDC. It has two globular C1q domains and a signal peptide and can act either as an opsonin and facilitate the phagocytosis of nonself particles or as a cytokine and stimulate the degranulation of cytotoxic cells. In the present work, we used a commercial antibody raised against human CTRP4 (hCTRP4) to provide additional evidences of the involvement of this molecule in immune responses. The antibody was validated in immunoblot analysis and recognizes a band corresponding to the expected molecular weight inferred from the analysis of the amino acid sequence of BsC1qDC. The presence of the antibody in the culture medium in phagocytosis and degranulation assays significantly reduced the two responses. In addition, the relationships between complement C3 activation and bsc1qdc transcription was studied using the injection of C3aR agonist in the colonial vasculature.