Complement C4 is an important mediator of brain-death induced lung injury

J.E. van Zanden, N.M. Jager, F. Poppelaars, Z.J. Veldhuis, M.E. Erasmus, H.G.D. Leuvenink, M.A. Seelen

Wednesday 13 march 2019

14:14 - 14:16h at Koningin Máximazaal

Categories: Basaal, Parallelsessie

Parallel session: Parallelsessie III - Basaal I

Background: The process of brain death (BD) in multi-organ donors causes hemodynamic and hormonal dysregulation, leading to pulmonary inflammation. As a result, the quality of the lung graft is deteriorated and only 30% of potential donor lungs are suitable for transplantation. The complement system is known to play an important role in the BD-induced inflammatory response. Therapeutically targeting the complement system in donor grafts seems to be a promising method to improve donor organ quality and thereby graft survival. To do so, the specific role of complement molecules activated in brain-dead donor lungs needs to be elucidated. Our study was designed to identify which complement pathway(s) are involved in BD-induced lung injury.

Methods: In order to dissect contribution of the different complement components in BD-induced inflammation, wildtype (WT) mice were compared to complement deficient mice. The central complement component was studied in C3-/- mice, the classical and lectin pathway in C4-/- mice and the alternative pathway in factor Properdin-/- (P) mice. BD was induced by inflating a Fogarthy catheter in the epidural space, sustained for 3 hours under continuous blood pressure monitoring. Lungs were ventilated with a frequency of 190/min, tidal volume of 225 µl and a PEEP of 1 cmH₂O. Immunohistochemistry was performed to assess lung morphology, neutrophil infiltration and membrane-attack complex deposition as depicted by C9 staining. Gene expression for pro-inflammatory cytokines were measured by qPCR.

Results: Compared to WT mice, absence of C3 prevented C9 deposition, improved lung morphology, decreased neutrophil influx and significantly downregulated pro-inflammatory cytokines and chemokines. Those results suggest a promising role for central complement component blockade in lung grafts derived from brain-dead donors. Regarding the activation pathways, C4 seems mainly involved in BD-related lung injury. Lung morphology, neutrophil influx and pro-inflammatory gene expression levels were ameliorated in C4-/- compared to WT mice, and C9 deposition was diminished to a level comparable to sham-operated mice. P-/- mice showed improved morphology and decreased gene expressions, yet neutrophil influx and C9 deposition were not affected.

Conclusions: Those results suggest primary involvement of the classical/lectin complement pathway in the BD-induced pulmonary immune response, providing insight for future targeted complement blockade in potential donor lungs.