Postinjury complement C4 activation is associated with adverse outcomes and is potentially influenced by plasma resuscitation

Abstract

Background: Complement activation after trauma promotes hemostasis but is associated with increased morbidity and mortality. However, the specific pathways and downstream mediators remain unclear. Recently, the anaphylatoxin C4a has been shown to bind to thrombin receptors. While plasma-based resuscitation has been shown to modify the endotheliopathy of trauma, it may provide complement zymogens that fuel ongoing inflammatory cascades. We sought to characterize the activation of complement after injury and the effect of fresh frozen plasma (FFP) on this inflammatory response. We hypothesized that trauma induces C4 activation, which is associated with worse outcomes and influenced by FFP resuscitation.

Methods: Blood was collected from injured patients at a single level I trauma center enrolled in the Control of Major Bleeding after Trauma (COMBAT) randomized clinical trial. Proteomic analyses were performed through targeted liquid chromatography coupled with mass spectrometry. For the present observational study, concentrations of complement proteins were analyzed at multiple time points, compared between treatment groups, and correlated with outcomes.

Results: C4 activation occurred over the first 6 hours postinjury with peak activation 6 to 24 hours. Tissue hypoperfusion, defined as base deficit >10 mEq/L, and requirement for massive transfusion were associated with greater C4 activation. C4 activation was associated with mortality, multiple organ failure, and longer ventilator requirement. In addition, temporal trends of C1q, factor B, and C3 by outcome groups support the prevailing theory of primary classical pathway activation with alternative pathway amplification. Resuscitation with FFP over the first 6 hours was associated with increased C4 activation at 12 and 24 hours.

Conclusion: C4 activation has an important inflammatory role postinjury, and FFP has the potential to augment this complement activation during resuscitation.

Level of evidence: Prognostic/epidemiological, level III.

Figure 1.

Study Profile. COMBAT Trial (Control Of Major Bleeding After Trauma Trial).

Figure 2.

Massive transfusion was associated with C4 activation. A: C4 concentrations (least squares mean, label-free quantification) were significantly lower from 6–72 hours in those who required massive transfusion (P<0.05). B: C1q concentrations trended overall lower in those requiring massive transfusion (P=NS). C: C3 concentrations trended lower from 24–72 hours in those who required massive transfusion (P=NS). D: Factor B concentrations did not differ by massive transfusion requirement. Error bars represent standard error of the mean (SEM).

Figure 3.

Multiple organ failure (MOF) was associated with sustained activation of C4, C1q, C3, and factor B. A: C4 concentrations (least squares mean, label-free quantification) were lower in those developing MOF, significantly at 48hr (P<0.01). B: C1q concentrations trended lower overall in those developing MOF (P=NS). C and D: C3 and factor B concentrations were significantly lower at 48 and 72 hours in those developing MOF (P<0.01). Error bars represent standard error of the mean (SEM).

Figure 4.

Mortality was associated with C4 and C3 activation but not C1q or factor B. A: C4 concentrations (least squares mean, label-free quantification) were lower in non-survivors, significantly at 12 hours (P<0.05). B: C1q concentrations were no different by mortality: C: C3 concentrations trended lower in non-survivors from 24–72 hours (P=NS). D: Factor B concentrations were no different by mortality. Error bars represent standard error of the mean (SEM).

Figure 5.

C4 and C1q activation were associated with longer ventilator requirement. A: C4 concentrations (least squares mean, label-free quantification) were significantly lower from 6–72 hours in patients with ≤25 ventilator-free days (VFD) versus those with >25 VFD (P<0.05). B: C1q concentrations were significantly lower at four hours in patients with ≤25 VFD (P<0.05). C and D: C3 and factor B concentrations were no different in patients with ≤25 VFD. Error bars represent standard error of the mean (SEM).