Complement and complement regulatory proteins are upregulated in lungs of COVID-19 patients

We explored the pathological changes and the activation of local complement system in COVID-19 pneumonia. Lung paraffin sections of COVID-19 infected patients were analyzed by HE (hematoxylin-eosin) staining. The deposition of complement C3, the deposition of C3b/iC3b/C3d and C5b-9, and the expression of complement regulatory proteins, CD59, CD46 and CD55 were detected by immunohistochemistry. In COVID-19 patients' lung tissues, fibrin exudation, mixed with erythrocyte, alveolar macrophage and shed pneumocyte are usually observed in the alveoli. The formation of an "alveolar emboli" structure may contribute to thrombosis and consolidation in lung tissue. In addition, we also found that compared to normal tissue, the lung tissues of COVID-19 patients displayed the hyper-activation of complement that is represented by extensive deposition of C3, C3b/iC3b/C3d and C5b-9, and the increased expression level of complement regulatory proteins CD55, and especially CD59 but not CD46. The thrombosis and consolidation in lung tissues may contribute to the pathogenesis of COVID-19. The increased expression of CD55 and CD59 may reflect a feedback of self-protection on the complement hyper-activation. Further, the increased C3 deposition and the strongly activated complement system in lung tissues may suggest the rationale of complement-targeted therapeutics in conquering COVID-19.

Ayu (Plecoglossus altivelis) CD46 isoforms protect the cells from autologous complement attack

CD46 is an important immune regulatory receptor with multiple functions. However, studies on the function of teleost CD46, especially the different CD46 isoforms are limited. In this study, we identified three membrane cofactor protein (MCP, CD46) gene isoforms from ayu (Plecoglossus altivelis) and tentatively named as PaCD46 isoforms. PaCD46 isoforms were generated by alternative splicing and all consisted of four conserved short consensus repeats (SCRs), and the variable serine-threonine-proline-rich domain, transmembrane hydrophobic domain, and cytoplasmic tail. Phylogenetic analysis showed that the isoforms clustered together with other fish CD46 and then with higher animal CD46. Western blotting analysis of peripheral blood mononuclear cells (PBMC) revealed three bands, all of which had much larger molecular weights than the theoretical values of the three PaCD46 isoforms. Moreover, three PaCD46 isoforms were individually expressed on HEK293 cells, and Western blotting showed the similar band profile to that of PBMC. The recombinant extracellular domain of the PaCD46 isoforms, obtained by expression in Pichia pastoris, significantly reduced hemolysis activity of ayu sera. Furthermore, each of the three PaCD46 isoforms respectively protected the HEK293 cells expressing the isoform. The isoforms were also identified for their protection of autologous PBMC from complement activation. These results provided the first evidence that PaCD46 isoforms may be complement regulatory proteins to prevent complement-induced damage to self-tissue.

Whole-exome sequencing detects mutations in pediatric patients with atypical hemolytic uremic syndrome in Taiwan

Although atypical hemolytic uremic syndrome (aHUS) is a genetic disorder, molecular defects are detected in only 60% of patients. We aim to dissect the genetic background by whole exome sequence and the clinical characteristics of pediatric patients with aHUS. Ten patients (6 male and 4 female) with mean age 5.2 ± 5.0 years were enrolled. The age at onset ranged from 2 days to 11 years. Eighteen different mutations (17 missense, 2 nonsense, and 11 novel) on 7 complement and 3 coagulation genes were detected in all patients. The majority of mutation was heterozygous and S1191L on CFH were the recurrent mutation. Sixty percent of patients had multiple genetic mutations. Nine mutations were associated with genes known to be implicated in aHUS (CFH, CFI, CD46, CFHR5, and DGKE), while 4 and 5 mutations were detected on complement- (C8B, C9, and MASP1) and coagulation-associated (VWF and CD36) genes, respectively. CD36 may be a candidate gene act as disease modifier for aHUS through the contribution of thrombosis by impairing the interaction with TSP-1 and ADAMTS 13 shown in simulation model. Genetic defects on both complement and coagulation pathways play pathogenic roles on aHUS. CD36 may be a novel candidate gene act as disease modifier of aHUS.

Characterization of a teleost membrane-associated protein that is involved in the regulation of complement activation and bacterial infection

In mammals, membrane-associated complement regulatory proteins (MCRP) can protect host cells from the damaging of the activated complement. In teleost, few studies on the function of MCRP have been documented. In the present report, we identified a MCRP (named CsMCRP) from the teleost fish tongue sole Cynoglossus semilaevis and examined its immune function. CsMCRP shares moderate sequence identities with fish DAF-like molecules. CsMCRP was predicted to be a transmembrane protein with three short consensus repeats located in the extracellular region. CsMCRP expression occurred in nine different tissues, especially blood, and in peripheral blood leukocytes (PBL). Recombinant CsMCRP inhibited complement activation and interacted with bacterial pathogen, the latter in a highly selective manner. Antibody blocking the CsMCRP on PBL significantly inhibited bacterial infection of PBL. These results indicate that teleost CsMCRP is both a regulator of complement activation and a cellular receptor involved in bacterial invasion.

Modulation of PBMC-decay accelerating factor (PBMC-DAF) and cytokines in rheumatoid arthritis

Studies have suggested that abnormal expression of complement regulatory proteins and cytokines contribute significantly to the path-physiology of rheumatoid arthritis. In this context, Decay accelerating factor (DAF) a complement regulatory protein is gaining increased attention. With the notion that immune effecter mechanisms are all interlinked and circulating peripheral blood mononuclear cells (PBMCs) should have a role in a systemic disease like rheumatoid arthritis, we studied the modulation and significance of PBMC-DAF and cytokines in RA. Seventy-five RA patients and 75 healthy controls were recruited. Expression of DAF and cytokines (IFN-γ, IL-17A and IL-10) in the PBMCs of patients and controls was determined. Correlations among DAF, cytokines, and disease activity were evaluated by standard statistical methods. The effect of IFN-γ, IL-17A, and IL-10 on the expression of DAF in patients and controls was studied in vitro. Expression of PBMC-DAF declined in patients both at mRNA and surface level and correlated negatively with the disease activity. Expression of IFN-γ also declined in patients but correlated positively with DAF and negatively with disease activity. Expression of IL-17A and IL-10 was higher in patients. The levels correlated positively with disease activity and negatively with DAF both in patients and controls. In vitro studies indicated that IFN-γ up-regulated DAF expression in PBMCs, whereas IL-17A and IL-10 had negative effect on the same. The decline in the PBMC-DAF is a contributing factor in manifestations of RA. Cytokine environment contributes to this decline. These findings brought novel insights into the complement-cytokine axis in the path-physiology of RA.

Complement regulatory protein genes in channel catfish and their involvement in disease defense response

Complement system is one of the most important defense systems of innate immunity, which plays a crucial role in disease defense responses in channel catfish. However, inappropriate and excessive complement activation could lead to potential damage to the host cells. Therefore the complement system is controlled by a set of complement regulatory proteins to allow normal defensive functions, but prevent hazardous complement activation to host tissues. In this study, we identified nine complement regulatory protein genes from the channel catfish genome. Phylogenetic and syntenic analyses were conducted to determine their orthology relationships, supporting their correct annotation and potential functional inferences. The expression profiles of the complement regulatory protein genes were determined in channel catfish healthy tissues and after infection with the two main bacterial pathogens, Edwardsiella ictaluri and Flavobacterium columnare. The vast majority of complement regulatory protein genes were significantly regulated after bacterial infections, but interestingly were generally up-regulated after E. ictaluri infection while mostly down-regulated after F. columnare infection, suggesting a pathogen-specific pattern of regulation. Collectively, these findings suggested that complement regulatory protein genes may play complex roles in the host immune responses to bacterial pathogens in channel catfish.

Complement regulatory proteins (CD46, 55 and 59) expressed on Schwann cells: immune targets in demyelinating neuropathies?

Given their localization and important role in regulating complement, complement regulatory proteins may act as target antigens and their antibodies as biomarkers in demyelinating neuropathies. We investigated the binding of autoantibodies to complement regulatory proteins (CD46, 55 and 59) in demyelinating diseases. In 42 acute inflammatory demyelinating polyneuropathy, 23 chronic inflammatory demyelinating polyneuropathy, 13 acute motor axonal neuropathy, 71 multiple sclerosis, and 19 neuromyelitis optica patients as well as 55 healthy controls, we were unable to detect significant titers of antibodies to CD46, CD55 and CD59. These autoantibodies are unlikely to be biomarkers in acute and chronic inflammatory demyelinating polyneuropathies.

Effect of eculizumab and recombinant human soluble thrombomodulin combination therapy in a 7-year-old girl with atypical hemolytic uremic syndrome due to anti-factor H autoantibodies

Atypical hemolytic uremic syndrome (aHUS), which is defined as non-Shiga toxin-associated hemolytic uremic syndrome, is a type of thrombotic microangiopathy. This syndrome presents with hemolytic anemia, thrombocytopenia, and acute kidney injury. Excessive complement activation due to genetic disorders of the complement system or production of autoantibodies to factor H (FH) causes the disease. We report a successful treatment course using eculizumab and recombinant human soluble thrombomodulin (rTMD) for a 7-year-old girl with aHUS due to anti-FH autoantibodies. Although her chief complaints were abdominal pain and loose stools, we were finally able to diagnose her with aHUS because Shiga toxin-producing Escherichia coli was not detected in her feces and a hemolytic assay analyzing FH function was positive. We administrated rTMD to our patient because of signs of disseminated intravascular coagulation. Soon after the therapeutic intervention, the platelet count began to increase and abdominal pain was moderately improved. Plasma exchange limited the efficacy of her disease. Therefore, we administered eculizumab, monoclonal humanized antibody against C5, 3 weeks after admission. Platelet counts immediately increased and kidney function gradually recovered. Genetic disorders were not detected. However, anti-FH autoantibody was observed. There were no symptoms for recurrence of aHUS or kidney dysfunction for 15 months, as a result of the administration of eculizumab every other week. In conclusion, combination therapy of eculizumab and rTMD was effective for an aHUS patient. This therapy may be helpful for improving the prognosis and long-term kidney function of aHUS patients.