If the COVID-19 pandemic has done one thing, it’s made us all more familiar with some of the important players in the immune system. Antibodies, B cells, and T cells are among the best known parts of the body’s response to a virus like SARS-CoV-2, but they don’t act alone.
In a paper published on August 18 in the journal Cell, scientists report that innate immune cells—a critical part of the immune system activated to battle COVID-19—remain altered for at least a year after infection. The finding suggests that these cells may play a role in some of the lingering symptoms associated with Long COVID, although more studies are needed to confirm that connection.
The innate immune system is the body’s first line of defense, made up of general pathogen-fighting cells that are designed to recognize and fight off all kinds of pathogens, including bacteria, viruses, fungi, and parasites in a non-specific way. (B cells and T cells, in contrast, are more customized to remember and recognize specific pathogens, and only those pathogens.) Steven Josefowicz, an associate professor of pathology and laboratory medicine at Weill Cornell Medical College, and his colleagues found, however, that even innate immune cells retain some memory of fighting SARS-CoV-2 after a severe infection. This recall, and the response it generates, can last for at least a year after infection.
The new paper has important implications for understanding how the immune system—even the less bespoke parts that aren’t targeting specific bacteria or viruses—is changed by infections. Understanding these alterations could also shed light on why some people continue to experience long-term symptoms after encountering SARS-CoV-2, says Josefowicz.
One thing the COVID-19 pandemic has done is to introduce us all to some important elements of the immune system. Antibodies, B cells and T cells are among the best-known parts of the body’s response to viruses such as SARS-CoV-2, but they do not all act alone.
In a paper published August 18 in the journal Cell, scientists report that innate immune cells – a key part of the immune system activated to fight COVID-19 – remain replaceable for at least a year after infection. The finding suggested that these cells may play a role in some of the symptoms associated with long Covid-19, although more studies are needed to confirm that connection.
The innate immune system is the body’s first line of defense, made up of normal pathogen-fighting cells that are designed to non-specifically recognize and fight all types of pathogens, including bacteria, viruses, fungi, and parasites. Has gone. (In contrast, B cells and T cells are more optimized to remember and recognize specific pathogens and only those pathogens.) Steven Josephovich, MD, an associate professor of pathology and laboratory medicine at Weill Cornell Medical College, and his colleagues found, however, that Even innate immune cells retain some memory of fighting SARS-CoV-2 after severe infection. This memory, and the response it produces, can persist for at least a year after infection.
The new paper has important implications for understanding how the immune system – even the less specific parts that aren’t targeting specific bacteria or viruses – are altered by infection. Understanding these changes may also shed light on why some people continue to experience long-term symptoms after exposure to SARS-CoV-2, says Josephowicz.
He and his team focused on the progenitor cells of innate immune cells — stem cells in the bone marrow that continually replenish the supply of these immune cells. Since most of these stem cells reside in the bone marrow, the easiest way to access them is through bone marrow aspiration, a painful and invasive procedure in which doctors make a hole in a section of the hip bone to access the marrow. However, a small number of these stem cells circulate in the blood, and Josephowicz conducted the study not only to extract and enrich their numbers from blood samples, but also to confirm that they are the same stem cells found in the marrow. represent. This allowed them to study these cells from patients who had been admitted to the ICU with severe COVID-19 infection, by collecting their blood, rather than obtaining bone marrow biopsies.
By analyzing those stem cells, “it is clear that the immune system is fundamentally altered after a severe infection such as COVID-19,” he says. These cells have genetic mutations that alter the genes they express, causing them to produce more inflammatory factors. The changes last at least a year after severe COVID-19 infection, which is what Josephowicz studied in cells from a few dozen patients. Since these stem cells are responsible for making more copies of the innate immune cells, changes in the genes they express are carried over to new generations of cells created by them. When he studied the cells in a dish, Josephowicz found that they were able to produce higher levels of inflammatory factors and were more likely to migrate—which in the human body means they can transmit their inflammatory effects to other cells. Can spread to tissues. In animal models, these highly reactive cells are preferentially attracted to the lungs, brain and heart, some of the organs most affected by prolonged COVID.
High levels of inflammatory factors may be a response to the acute effects of severe SARS-CoV-2 infection. “Severe COVID-19 may make the immune system see the beginning of a long-term infection,” says Josephowicz, “and since the immune system is having trouble clearing this particular pathogen, it may try to give itself a better chance.” Everyone is trying. Dealing with the virus.”
Whether this memory of COVID-19 is contributing to long COVID is not yet clear, but the research may inspire additional studies to better understand how viruses such as SARS-CoV-2 affect both the short-term and the long-term. How do they affect the immune system? “This is the beginning of a very long story that will hopefully open up our understanding of how viral infections, and COVID-19 in particular, differ from colds,” says Dr. Lindsay Leaf, director of the Medical ICU and Post ICU. Recovery Clinic at Weill Cornell New York Presbyterian Hospital and one of the paper’s co-authors. “We need to understand how infection changes the immune system, thereby affecting not only your symptoms, but how you respond to your next infection or your next vaccination.”
