Complement system and phagocytosis in a colonial protochordate.

Area of Science:

• Marine biology
• Immunology
• Cell biology

Background:

• Phagocytosis is a critical cellular process for immune defense and tissue homeostasis.
• The complement system, particularly C3, is known to be involved in immune responses in various organisms.
• The role of complement C3 in phagocytosis within invertebrate models like Botryllus schlosseri remains underexplored.

Purpose of the Study:

• To investigate the function of complement C3 (BsC3) in phagocytosis in the colonial ascidian Botryllus schlosseri.
• To examine the transcriptional modulation of BsC3 during the colonial blastogenetic cycle, focusing on the takeover phase.
• To determine the involvement of BsC3 in the clearance of apoptotic cells by phagocytes.

Main Methods:

• In situ hybridization using BsC3 riboprobes to identify BsC3-expressing cells.
• Immunohistochemistry with anti-human C3 antibody to detect C3 localization in haemocytes.
• Phagocytosis assays using haemocytes from colonies treated with anti-hC3 antibody or BsC3 siRNA to assess phagocytic capacity.

Main Results:

• BsC3 transcription was detected in morula cells, the most abundant haemocytes.
• Inhibition of C3 activation significantly reduced the phagocytic capability of haemocytes.
• Phagocytes were identified as key players in BsC3-mediated phagocytosis.

Conclusions:

• Complement C3 (BsC3) plays a significant role in mediating phagocytosis in Botryllus schlosseri.
• BsC3 is involved in the clearance of apoptotic cells during the colonial takeover.
• Further research is warranted to identify the specific receptors for BsC3 activation products.