Posts Tagged ‘complement’

Is SARS-COV2 Hijacking the Complement and Coagulation Systems?

Reporter: Stephen J. Williams, PhD

In a recent Nature Medicine paper “Immune complement and coagulation dysfunction in adverse outcomes of SARS-CoV-2 infection” Ramlall et al. demonstrate, in a retrospective study, that a significant number of patients presenting SARS-CoV2 complications had prior incidences of macular degeneration and coagulation disorders and these previous indications are risk factors for COVID-related complications.



Understanding the pathophysiology of SARS-CoV-2 infection is critical for therapeutic and public health strategies. Viral–host interactions can guide discovery of disease regulators, and protein structure function analysis points to several immune pathways, including complement and coagulation, as targets of coronaviruses. To determine whether conditions associated with dysregulated complement or coagulation systems impact disease, we performed a retrospective observational study and found that history of macular degeneration (a proxy for complement-activation disorders) and history of coagulation disorders (thrombocytopenia, thrombosis and hemorrhage) are risk factors for SARS-CoV-2-associated morbidity and mortality—effects that are independent of age, sex or history of smoking. Transcriptional profiling of nasopharyngeal swabs demonstrated that in addition to type-I interferon and interleukin-6-dependent inflammatory responses, infection results in robust engagement of the complement and coagulation pathways. Finally, in a candidate-driven genetic association study of severe SARS-CoV-2 disease, we identified putative complement and coagulation-associated loci including missense, eQTL and sQTL variants of critical complement and coagulation regulators. In addition to providing evidence that complement function modulates SARS-CoV-2 infection outcome, the data point to putative transcriptional genetic markers of susceptibility. The results highlight the value of using a multimodal analytical approach to reveal determinants and predictors of immunity, susceptibility and clinical outcome associated with infection.


As part of a separate study, the authors mapped over 140 cellular proteins that are structurally mimicked by coronaviruses (CoVs) and identified complement and coagulation pathways as targets of this strategy across all CoV strains4. The complement system is a critical defense against pathogens, including viruses5 and when dysregulated (by germline variants or acquired through age-related effects or excessive tissue damage) can contribute to pathologies mediated by inflammation5,6,7.

“So, virally encoded structural mimics of complement and coagulation factors may contribute to CoV-associated immune-mediated pathology and indicate sensitivities in antiviral defenses.”


Methods and Results

  • Between 1 February 2020 and 25 April 2020, 11,116 patients presented to New York-Presbyterian/Columbia University Irving Medical Center with suspected SARS-CoV-2 infection, of which 6,398 tested positive
  • Electronic health records (EHRs) were used to define sex, age and smoking history status as well as histories of macular degeneration, coagulatory disorders (thrombocytopenia, thrombosis and hemorrhage), hypertension, type 2 diabetes (T2D), coronary artery disease (CAD) and obesity (see Methods). A Python algorithm was used to analyze all confounders.
  • identified 88 patients with history of macular degeneration, 4 with complement deficiency disorders and 1,179 with coagulatory disorders).
  • observed a 35% mortality rate among patients that were put on mechanical ventilation and that 31% of deceased patients had been on mechanical respiration.
  • patients with AMD (a proxy for complement activation disorders) and coagulation disorders (thrombocytopenia, thrombosis and hemorrhage) were at significantly increased risk of adverse clinical outcomes (including mechanical respiration and death) following SARS-CoV-2 infection
  • 650 NP swabs from control and SARS-CoV-2-infected patients who presented to Weill-Cornell Medical Center were evaluated by RNA-Seq. Gene set enrichment analysis (GSEA) of Hallmark gene sets found that SARS-CoV-2 infection (as defined by presence of SARS-CoV-2 RNA and stratified into ‘positive’, ‘low’, ‘medium’ or ‘high’ based on viral load; induces genes related to pathways with known immune modulatory functions (Fig. 2a). Moreover, among the most enriched gene sets, SARS-CoV-2 infection induces robust activation of the complement cascade (false discovery rate (FDR) P < 0.001), with increasing enrichment and significance with viral load (FDR P < 0.0001).
  • KEGG Pathway Analysis revealed KEGG_Complement_and_Coagulation_Cascades’, ‘GO_Coagulation’ and ‘Reactome_initial_triggering_of_complement’ to be significantly enriched in expression profiles of SARS-CoV-2-infected samples
  • conducted a candidate-driven study to evaluate whether genetic variation within a 60-Kb window around 102 genes with known roles in regulating complement or coagulation cascades (2,888 genetic variants fulfill this criteria of the 805,426 profiled in the UK Biobank) is associated with poor SARS-CoV-2 clinical outcome
  • identified 11 loci representing seven genes with study-wide significance. A variant of coagulation factor III (F3), variant rs72729504, was found to be associated with increased risk of adverse clinical outcome associated with SARS-CoV-2 infection. The analysis also identified that four variants previously reported to be associated with AMD (rs45574833, rs61821114, rs61821041 and rs12064775)15predispose carriers to hospitalization following SARS-CoV-2 infection

As authors state:

“Among the implications, the data warrant heightened public health awareness for the most vulnerable individuals and further investigation into an existing menu of complement and coagulation targeting therapies that were recently shown to be beneficial in a small cohort of patients with SARS-CoV-2 infection.” 26,27.



Ramlall, V., Thangaraj, P.M., Meydan, C. et al. Immune complement and coagulation dysfunction in adverse outcomes of SARS-CoV-2 infection. Nat Med (2020). https://doi.org/10.1038/s41591-020-1021-2



Lasso, G., Honig, B. & Shapira, S. D. A sweep of earth’s virome reveals host-guided viral protein structural mimicry; with implications for human disease. Preprint at bioRxiv https://doi.org/10.1101/2020.06.18.159467 (2020).



Viruses deploy an array of genetically encoded strategies to coopt host machinery and support viral replicative cycles. Molecular mimicry, manifested by structural similarity between viral and endogenous host proteins, allow viruses to harness or disrupt cellular functions including nucleic acid metabolism and modulation of immune responses. Here, we use protein structure similarity to scan for virally encoded structure mimics across thousands of catalogued viruses and hosts spanning broad ecological niches and taxonomic range, including bacteria, plants and fungi, invertebrates and vertebrates. Our survey identified over 6,000,000 instances of structural mimicry, the vast majority of which (>70%) cannot be discerned through protein sequence. The results point to molecular mimicry as a pervasive strategy employed by viruses and indicate that the protein structure space used by a given virus is dictated by the host proteome. Interrogation of proteins mimicked by human-infecting viruses points to broad diversification of cellular pathways targeted via structural mimicry, identifies biological processes that may underly autoimmune disorders, and reveals virally encoded mimics that may be leveraged to engineer synthetic metabolic circuits or may serve as targets for therapeutics. Moreover, the manner and degree to which viruses exploit molecular mimicry varies by genome size and nucleic acid type, with ssRNA viruses circumventing limitations of their small genomes by mimicking human proteins to a greater extent than their large dsDNA counterparts. Finally, we identified over 140 cellular proteins that are mimicked by CoV, providing clues about cellular processes driving the pathogenesis of the ongoing COVID-19 pandemic.



Risitano, A. M. Complement as a target in COVID-19?. Nat. Rev. Immunol. 20, 343–344 (2020).



Mastaglio, S. et al. The first case of COVID-19 treated with the complement C3 inhibitor AMY-101. Clin. Immunol. 215, 108450 (2020).



Polubriaginof, F. C. G. et al. Challenges with quality of race and ethnicity data in observational databases. J. Am. Med. Inf. Assoc. 26, 730–736 (2019).


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