Inhibition of Immune Complex Complement Activation and Neutrophil Extracellular Trap Formation by Peptide Inhibitor of Complement C1

Pamela S Hair,Kenji M Cunnion,Neel K Krishna,Adrianne I Enos

doi:10.3389/fimmu.2018.00558

Abstract

Two major aspects of systemic lupus erythematosus (SLE) pathogenesis that have yet to be targeted therapeutically are immune complex-initiated complement activation and neutrophil extracellular trap (NET) formation by neutrophils. Here, we report in vitro testing of peptide inhibitor of complement C1 (PIC1) in assays of immune complex-mediated complement activation in human sera and assays for NET formation by human neutrophils. The lead PIC1 derivative, PA-dPEG24, was able to dose-dependently inhibit complement activation initiated by multiple types of immune complexes (IC), including C1-anti-C1q IC, limiting the generation of pro-inflammatory complement effectors, including C5a and membrane attack complex (sC5b-9). In several instances, PA-dPEG24 achieved complete inhibition with complement effector levels equivalent to background. PA-dPEG24 was also able to dose-dependently inhibit NET formation by human neutrophils stimulated by PMA, MPO, or immune complex activated human sera. In several instances PA-dPEG24 achieved complete inhibition with NETosis with quantitation equivalent to background levels. These results suggest that PA-dPEG24 inhibition of NETs occurs by blocking the MPO pathway of NET formation. Together these results demonstrate that PA-dPEG24 can inhibit immune complex activation of the complement system and NET formation. This provides proof of concept that peptides can potentially be developed to inhibit these two important contributors to rheumatologic pathology that are currently untargeted by available therapies.

Highlights

The pathogenesis of systemic lupus erythematosus (SLE) is very complex, but two major contributors are immune complex-initiated complement activation and neutrophil extracellular trap (NET) formation
For C5a, 1 mM PA-dPEG24 lead to a 61% reduction (p = 0.002) compared with heat-aggregated IgG (Agg-IgG) with no inhibitor. These results suggest that PA-dPEG24 can inhibit immune complex-initiated complement activation in human sera
The experiments shown above demonstrate that PA-dPEG24 can inhibit immune complex-initiated complement activation and the generation of pro-inflammatory complement effectors

Summary

Introduction

The pathogenesis of systemic lupus erythematosus (SLE) is very complex, but two major contributors are immune complex-initiated complement activation and neutrophil extracellular trap (NET) formation. Immune complexes (IC) initiating classical pathway complement activation leading to consumption of C4 and C3 have long been appreciated and clearly contribute to lupus nephritis [1,2,3]. The role of anti-C1q antibodies in the blood of SLE patients is an active area of investigation with considerable data accumulating to demonstrate a strong association between the presence of anti-C1q antibodies and lupus nephritis [7, 8]. Investigators have shown that anti-C1q antibodies from SLE patients bound to a surface in an ELISA-type assay can activate the classical and lectin pathways [9]. Anti-C1q antibodies appear to be important in pathogenesis and deserve consideration when modeling SLElike IC

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Conclusion