Functional roles for C5a receptors in sepsis

Area of Science:

• Immunology
• Molecular Biology
• Pathophysiology

Background:

• The precise roles of complement component 5a (C5a) receptors, C5a receptor (C5ar) and C5a-like 2 (C5l2), in inflammatory conditions like sepsis are not fully understood.
• C5l2 has been controversially described as a 'default receptor', lacking clear signaling capabilities.

Purpose of the Study:

• To elucidate the individual and combined roles of C5ar and C5l2 in polymicrobial sepsis induced by cecal ligation and puncture (CLP).
• To investigate the involvement of these receptors in the release of high mobility group box 1 protein (HMGB1) during sepsis.

Main Methods:

• Utilized antibody-induced blockade of C5a receptors in a mouse model of CLP.
• Employed knockout mice lacking either C5ar or C5l2 to assess receptor function.
• Measured survival rates and quantified proinflammatory mediators in plasma.
• Assessed the in vivo and in vitro release of HMGB1.

Main Results:

• In moderate sepsis, blockade or genetic absence of either C5ar or C5l2 significantly enhanced survival and reduced plasma proinflammatory mediators.
• C5l2, but not C5ar, was essential for both in vivo and in vitro release of HMGB1.
• In severe sepsis, only the combined blockade of both C5ar and C5l2 conferred protection.

Conclusions:

• C5ar and C5l2 act synergistically to exacerbate the detrimental effects of sepsis.
• C5l2 is a functional receptor critically involved in HMGB1 release, challenging its prior designation as a 'default receptor'.