Complement Membrane Attack Complexes Assemble NLRP3 Inflammasomes Triggering IL-1 Activation of IFN-γ-Primed Human Endothelium

Rationale: Complement activation contributes to multiple immune-mediated pathologies. In late allograft failure, donor-specific antibody deposits complement membrane attack complexes (MAC) on graft endothelial cells (ECs), substantially increasing their immunogenicity without causing lysis. Internalized MAC stabilize NF-κB-inducing kinase (NIK) protein on Rab5+MAC+ endosomes, activating non-canonical NF-κB signaling. However, the link to increased immunogenicity is unclear. Objective: To identify mechanisms by which alloantibody and internalized MAC activate ECs to enhance their ability to increase T cell responses.Methods and Results: In human EC cultures, internalized MAC also causes NLRP3 translocation from endoplasmic reticulum to Rab5+MAC+NIK+ endosomes followed by endosomal NIK-dependent inflammasome assembly. Cytosolic NIK, stabilized by LIGHT, does not trigger inflammasome assembly and ATP-triggered inflammasome assembly does not require NIK. IFN-γ primes EC responsiveness to MAC by increasing NLR...