20 - ROLE OF COMPLEMENT SYSTEM IN THE LCWE-INDUCED MURINE MODEL OF KAWASAKI DISEASE VASCULITIS

Background: Several studies have implicated activation of the complement system in patients with KD. The complement system is a major component of innate immunity and consists of both soluble factors and cell surface receptors that interact to sense and respond to invading pathogens and functions as an immune surveillance system that rapidly responds to infections. The three arms of the complement pathway (classical, alternative and mannose binding lectin) converge on C3 and C5 activation and induce complement protein deposition on bacterial or viral walls for clearance. Importantly, complement components can exacerbate pro-inflammatory signaling and IL-1β production.The central complement component, C3, is an opsonizing factor which labels its microbial targets for clearance by phagocytes. We aim to investigate the role of the complement system in the Lactobacillus casei cell wall extract (LCWE)-induced murine model of KD vasculitis.

Methods: We investigated the development of LCWE-induced vasculitis when complement fragments are blocked. We measured heart inflammation scores and abdominal aorta dilation in control or LCWE-injected wild type or C3-deficient mice or mice treated with the C5aR1 antagonist PMX205. We performed immunofluorescence staining of C3aR1 and C5aR1 in hearts and abdominal aortas in mice to quantify the levels of these receptors during LCWE-induced KD. We also quantified the expression of complement products in serum by qRT-PCR. We took advantage of published human gene expression datasets to quantify the levels of complement fragments in the blood of control or KD patients. Furthermore, we performed an ELISA-assay to show deposition of C3 to LCWE for clearance.

Results: We show that LCWE-injected mice have higher complement cleavage products in the serum, indicating activation. Since the three arms of the complement system (classical, alternative and lectin) converge on C3 and C5 activation, we checked their receptors, C3aR1 and C5aR1, and observed significant increase in their mRNA expression. Moreover, LCWE-injection in C3 deficient mice led to exacerbated cardiovascular lesions. Likewise, C5aR1 antagonist PMX205 injection increased the severity of the cardiovascular lesions in this model of KD. We also show that LCWE binds significantly less to C3 in heat inactivated or C3 deficient serum in our ELISA assay.

Conclusion: Based on our data, we show that blocking the activity of complement system exacerbates LCWE-induced KD vasculitis, potentially by impairing clearance of bacterial components via C3. Our studies reveal the contribution of the complement system in regulating innate immune response during LCWE-induced KD vasculitis, and potential novel markers.