Tag: complement proteins

Categories : COVID Immune SystemTags : Leave a comment

SARS-CoV-2 Hijacks Three Key Proteins in the Complement System

On By ModernMedia
SARS-CoV-2 viruses (yellow) infecting a human cell (blue). Photo by CDC on Pexels

Researchers at the Medical University of Vienna and the Medical University of Innsbruck discovered that SARS-CoV-2 hijacks three important host proteins that dampen the activity of the complement system, a key component of early antiviral immunity. This significantly impairs viral clearance which may affect the course of both acute COVID infections and post-COVID sequelae. The study was recently published in the journal Emerging Microbes & Infections.

An early and effective immune response is crucial for resolving viral infections and preventing post-infectious complications. The complement system, a pivotal element of antiviral immunity, is a cascade of proteins found in the bloodstream and at mucosal sites, such as the respiratory tract. Activated through three different pathways, complement facilitates the clearance of virus particles by directly inducing their destruction (lysis). To prevent bystander damage to host cells, complement is rapidly inactivated by a set of host molecules referred to as complement regulatory proteins. The new study led by Anna Ohradanova-Repic and colleagues from the Center for Pathophysiology, Infectiology and Immunology at the Medical University of Vienna in collaboration with the team of Heribert Stoiber from the Institute of Virology at the Medical University of Innsbruck shows that SARS-CoV-2 hijacks three of these regulatory proteins, CD55, CD59 and Factor H, and thereby successfully shields itself from complement-mediated lysis.

Hijacking host proteins for effective complement resistance

By propagating SARS-CoV-2 in human cells the researchers discovered that the virus particles acquire the cellular proteins CD55 and CD59. Further experiments showed that SARS-CoV-2 also binds to Factor H, another complement regulatory protein that is primarily found in the bloodstream. Confronting the virus particles with active complement revealed that they are partially resistant to complement-mediated lysis. By removing CD55, CD59 and Factor H from the virus surface or inhibiting their biological functions, the researchers could successfully restore complement-mediated clearance of SARS-CoV-2.

“Through hijacking these three proteins, SARS-CoV-2 can evade all three complement pathways, resulting in reduced or delayed viral clearance by the infected host,” Anna Ohradanova-Repic, the leader of the study explains. Because complement is intricately linked with other components of the immune system, this not only affects virus elimination but can also cause significant inflammation, a core feature of both severe COVID-19 and Long COVID. “Uncovering immune evasion mechanisms that allow the virus to linger within the host for longer, deepen our understanding of the acute and long-term impacts of SARS-CoV-2 infection,” says first author Laura Gebetsberger.

Source: Medical University of Vienna

Categories : COVID Immune SystemTags :

Overactive Complement System Causes Long Covid

On By ModernMedia
Photo by Andrea Piacquadio: https://www.pexels.com/photo/woman-in-gray-tank-top-3812757/

A new study from the University of Zurich (UZH) has revealed that the complement system plays an important role in Long Covid, a common sequela of SARS-CoV-2 infection. The findings, published in Science, show that the complement system ends up damaging tissue and blood cells even after the original infection has ended.

A significant proportion of individuals infected with SARS-CoV-2 develop long-lasting symptoms with a wide range of manifestations. The causes and disease mechanisms of Long Covid are still unknown, and there are no diagnostic tests or targeted treatments.

Part of the immune system active for too long

A team of researchers led by Onur Boyman, professor of immunology at UZH and Director of the Department of Immunology at the University Hospital Zurich (USZ), has implicated the complement system. It is part of the innate immune system and normally helps to fight infections and eliminate damaged and infected body cells.

“In patients with Long Covid, the complement system no longer returns to its basal state, but remains activated and, thus, also damages healthy body cells,” says Boyman.

Continued activation of complement system damages tissue and blood cells

The researchers followed 113 COVID patients for up to one year after their acute SARS-CoV-2 infection and compared them with 39 healthy controls.

After six months, 40 patients had active Long Covid disease.

More than 6500 proteins in the blood of the study participants were analysed both during the acute infection and six months later.

“The analyses of which proteins were altered in Long Covid confirmed the excessive activity of the complement system. Patients with active Long Covid disease also had elevated blood levels indicating damage to various body cells, including red blood cells, platelets and blood vessels,” explains Carlo Cervia-Hasler, a postdoctoral researcher in Boyman’s team and first author of the study.

Bioinformatics recognises protein patterns

The measurable changes in blood proteins in active Long Covid indicate an interaction between proteins of the complement system, which are involved in blood clotting and the repair of tissue damage and inflammation.

In contrast, the blood levels of Long Covid patients who recovered from the disease returned to normal within six months.

Active Long Covid is therefore characterised by the protein pattern in the blood.

The blood markers were discovered using bioinformatics methods in collaboration with Karsten Borgwardt during his time as a professor at ETH Zurich.

“Our work not only lays the foundation for better diagnosis, but also supports clinical research into substances that could be used to regulate the complement system. This opens up new avenues for the development of more targeted therapies for patients with Long Covid,” Onur Boyman said.

Source: University of Zurich

Categories : Medical Research & TechnologyTags :

New Coating Makes the Nanomedicine Go Down

On By ModernMedia
Upon injection into the blood, nanomedicines (blue spheres) are immediately attacked by proteins of the immune system called complement proteins (orange). Complement proteins cause rapid destruction of the nanomedicine, and also induce an anaphylaxis-like reaction. By attaching complement-degrading proteins (yellow ninjas made of protein) to the surface of nanomedicines, Penn researchers have largely solved this problem, potentially allowing more diseases to be safely treated by nanomedicine. Credit: University of Pennsylvania

In nanomedicine, immune reactions against the nanoparticles that contain the medicine or vaccine, reducing its effectiveness. Researchers have now come up with a new method to prevent the body from treating nanomedicines like foreign invaders, by covering those nanoparticles with a coating to suppress the immune response.

As soon as they are injected into the bloodstream, unmodified nanoparticles are swarmed by complement proteins, triggering an inflammatory response and preventing the nanoparticles from reaching their treatment targets. Penn Medicine researchers, whose findings are published in Advanced Materials, have devised a coating for nanoparticles that suppresses complement activation.

Nanoparticles are tiny capsules, typically made from proteins or fat-related molecules, that contain certain types of treatment or vaccine. The best-known examples of nanoparticle-delivered medicines are mRNA COVID vaccines.

“It turned out to be one of those technologies that just works right away and better than anticipated,” said study co-senior author Jacob Brenner, MD, PhD.

RNA- or DNA-based therapies generally need delivery systems to get them through the bloodstream into target organs. Harmless viruses often have been used as carriers or “vectors” of these therapies, but nanoparticles are increasingly considered safer alternatives. Nanoparticles also can be tagged with antibodies or other molecules that make them hone in precisely on targeted tissues.

The complement attack problem has been a serious impediment to nanomedicine. Circulating complement proteins treat nanoparticles as if they were bacteria, immediately coating nanoparticle surfaces and summoning macrophages to engulf them. Researchers have attempted to reduce the problem by pre-coating nanoparticles with camouflaging molecules, such as forming a watery, protective shell around nanoparticles using polyethylene glycol (PEG).

But nanoparticles camouflaged with substances like PEG still draw at least some complement attack. In general, nanoparticle-based medicines that move through the bloodstream (mRNA COVID vaccines are injected into muscle, not the bloodstream) have had a very low efficiency in getting to their target organs, usually under 1%.

In the study, the researchers came up with a new approach to protect nanoparticles, based on natural complement-inhibitor proteins that circulate in the blood, attaching to human cells to help protect them from complement attack.

In vitro tests using standard PEG-protected nanoparticles with one of these complement inhibitors, called Factor I, provided dramatically better protection from complement attack. In mice, the same strategy prolonged the half-life of standard nanoparticles in the bloodstream, allowing a much larger fraction of them to reach their targets.

“Many bacteria also coat themselves with these factors to protect against complement attack, so we decided to borrow that strategy for nanoparticles,” said co-senior author Jacob Myerson, PhD, a senior research scientist in the Department of Systems Pharmacology and Translational Therapeutics at Penn.

In a set of experiments in mouse models of severe inflammatory illness, the researchers also showed that attaching Factor I to nanoparticles prevents the hyper-allergic reaction that otherwise could be fatal.

Further testing will be needed before nanomedicines incorporating Factor I can be used in people, but in principle, the researchers said, attaching the complement-suppressing protein could make nanoparticles safer and more efficient as therapeutic delivery vehicles so that they could be used even in severely ill patients.

The researchers now plan other protective strategies for medical devices, such as catheters, stents and dialysis tubing, which are similarly susceptible to complement attack. They also plan to investigate other protective proteins.

“We’re recognising now that there’s a whole world of proteins that we can put on the surface of nanoparticles to defend them from immune attack,” Dr Brenner said.

Source: University of Pennsylvania School of Medicine