Complement levels in septic primates treated with anti-C5a antibodies.

Area of Science:

• Immunology
• Pathophysiology
• Pharmacology

Background:

• Gram-negative sepsis involves endotoxin activating the complement system.
• Complement anaphylatoxin C5a is implicated in neutrophil recruitment and lung injury, potentially causing adult respiratory distress syndrome.
• Understanding complement's role is crucial for developing sepsis treatments.

Purpose of the Study:

• To investigate the role of complement anaphylatoxin C5a in neutrophil-mediated lung injury during experimental gram-negative sepsis.
• To evaluate the efficacy of anti-C5a antibodies in mitigating septic shock and pulmonary edema in a primate model.
• To analyze complement component levels and activation pathways during sepsis.

Main Methods:

• Experimental sepsis was induced in primates via Escherichia coli infusion.
• Three groups were studied: control, septic, and septic treated with anti-human C5a antibodies.
• Complement component levels (C3, C4, C5) and anaphylatoxins (C3a, C4a, C5a) were measured using radial immunodiffusion and radioimmunoassay.

Main Results:

• Anti-C5a antibody treatment significantly attenuated septic shock and pulmonary edema.
• Septic groups showed depletion of C3, C4, and C5 complement levels, indicating both alternate and classical pathway activation.
• While early C3a and C4a levels were similar, peak C5a levels were 42% lower in the anti-C5a treated group, which did not elevate above control levels post-peak.
• The anti-human C5a antibody demonstrated cross-reactivity with primate C5a and specificity.

Conclusions:

• Complement anaphylatoxin C5a plays a critical role in sepsis-induced lung injury.
• Neutralization of C5a with specific antibodies can effectively reduce septic shock and pulmonary edema.
• Targeting C5a represents a promising therapeutic approach for managing severe sepsis and acute respiratory distress syndrome.