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A Fibrin-Enriched and tPA-Sensitive Photothrombotic Stroke Model

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In vivo-generated thrombin and plasmin do not activate the complement system in baboons.

Ravi S Keshari¹, Robert Silasi¹, Cristina Lupu¹

¹Cardiovascular Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK.

|October 13, 2017

Summary

Coagulation proteases like thrombin and plasmin do not directly activate the complement system in vivo. Bacterial infection, however, triggers complement activation during sepsis, independent of coagulation protease activity.

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Area of Science:

Biochemistry
Immunology
Hematology

Background:

Sepsis activates both coagulation and complement systems.
Coagulation proteases may directly cleave complement proteins, but in vivo evidence is limited.
Investigating direct protease-complement interactions is crucial for understanding sepsis pathogenesis.

Purpose of the Study:

To determine if in vivo generated coagulation proteases activate the complement cascade.
To compare complement activation in response to coagulation proteases versus bacterial challenge.
To investigate the role of thrombin, plasmin, and factor Xa in complement activation.

Main Methods:

Comparison of coagulation (TAT, PAP) and complement (C3b, C5a, C5b-9) biomarkers in baboons.
Infusion of factor Xa/phospholipids (FXa/PCPS) versus LD100 Escherichia coli.
Ex vivo serum incubation with coagulation enzymes.

Main Results:

Both FXa/PCPS and E. coli induced thrombin and plasmin generation.
Only E. coli challenge activated the complement system.
FXa/PCPS infusion did not lead to measurable complement activation in vivo.
Ex vivo studies showed complement cleavage only with supraphysiologic enzyme concentrations.

Conclusions:

In vivo-generated thrombin and plasmin do not directly activate the complement cascade in nonhuman primates.
Bacterial challenge, not coagulation proteases, drives complement activation in this sepsis model.
These findings challenge the hypothesis of direct protease-mediated complement activation in vivo.