Tag: immunity

Categories : Immune System Respiratory DiseasesTags :

Study Reveals Trained Immunity May Cause Lung Damage

On By ModernMedia

Discovery could help explain why some people are more vulnerable to lung damage during severe inflammation

Photo by Anna Shvets

Trained immunity – a process being explored in vaccine and therapy development to boost immune defences – appears to be counterproductive in certain contexts, researchers at McGill University and the Research Institute of the McGill University Health Centre (The Institute) have found.

Trained immunity is when the body’s first line of defence remembers past threats and becomes more reactive, responding more strongly to future infections even if they are different, by changing immune cells’ behaviour.

In an earlier study, the researchers had determined beta-glucan, a molecule found in the cell walls of fungi like yeast and mushrooms, can reduce lung damage during influenza infection. That study had focused on beta-glucan’s impact on neutrophils.

However, in a new study, published in the journal eLife, the team found exposure to beta-glucan can reprogram alveolar macrophages in a way that worsens lung damage during severe inflammation caused by viral or bacterial products. These cells help keep the lungs clean by clearing out dust, debris and pathogens.

“To date, most trained immunity research has focused on circulating immune cells that arise from the bone marrow,” said lead author Renaud Prével, a postdoctoral fellow at the Meakins-Christie Laboratories at The Institute. “We wanted to explore whether beta-glucan could induce trained immunity in alveolar macrophages, and whether that might be helpful or harmful.”

The researchers exposed mice to beta-glucan, which is known to trigger trained immunity and is found in some health supplements. A week later, the mice were exposed to signals that mimic severe viral or bacterial infections with sepsis-like phenotype. Using high-resolution microCT scans and fluid analysis, they found that mice given beta-glucan developed significantly more severe lung damage compared to the untreated control group.

To confirm the immune cells were causing the damage, researchers removed them from the mice, and the inflammation went away. When they put trained alveolar macrophages into other mice, the inflammation came back. The cells showed signs of immune training, but surprisingly, this didn’t happen through the usual immune pathways. It needed signals from infections and help from other immune cells.

“Our study shows that immune memory in the lungs is more dynamic than previously thought,” said senior author Maziar Divangahi, Professor of Medicine at McGill and Associate Director of the Meakins-Christie Laboratories. “This could help explain why some individuals develop more severe lung inflammation, especially in settings like sepsis.”

Source: McGill University

Categories : COVID Immune SystemTags :

Differences in Natural and Vaccine-induced COVID Immunity Revealed

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Source: Fusion Medical Animation on Unsplash

A new study recently published in Nature has found that immune protection resulting from COVID protection creates lasting effects in memory B cells.

Unlike circulating antibodies, which peak soon after vaccination or infection only to fade a few months later, memory B cells can remain to ward off severe disease for decades. They also evolve over time, learning to produce successively more potent ‘memory antibodies’ that are more effective at neutralising the virus and with better adaptation to variants.

Though vaccination instils higher levels of circulating antibodies than natural infection, the study suggests that not all memory B cells are created equal. While vaccination gives rise to memory B cells that evolve over a few weeks, natural infection births memory B cells that continue to evolve over several months, producing highly potent antibodies adept at eliminating even viral variants.

Though the findings suggest an advantage from natural infection over vaccination, this does not outweigh the dangers of illness and death from COVID, the researchers warn.

“While a natural infection may induce maturation of antibodies with broader activity than a vaccine does – a natural infection can also kill you,” explained Professor Michel C. Nussenzweig, head of Rockefeller’s Laboratory of Molecular Immunology. “A vaccine won’t do that and, in fact, protects against the risk of serious illness or death from infection.”

When any virus enters the body, immune cells immediately release circulating antibodies, which decay at variable rates depending on the vaccine or infection. They may confer protection for months or years but then dwindle in number, allowing possible reinfection.

Long term protection is provided by memory B cells that produce memory antibodies. Studies suggest that memory B cells for smallpox last at least 60 years after vaccination; those for Spanish flu, nearly a century. And while memory B cells don’t necessarily block reinfection, they can prevent severe disease.

Recent studies have suggested that within five months of receiving a vaccine or recovering from a natural infection, some no longer retain sufficient circulating antibodies to keep the novel coronavirus at bay, but memory B cells remain vigilant. Until now, however, scientists did not know whether the vaccines could be expected to provide the sort of robust memory B cell response seen after natural infection.

Prof Nussenzweig and colleagues resolved to tease out any differences in memory B cell evolution by comparing blood samples from convalescent COVID patients to those from never-infected mRNA-vaccinated individuals.

Vaccination and natural infection elicited similar numbers of memory B cells, which rapidly evolved between the first and second dose of the Pfizer and Moderna vaccines, producing increasingly potent memory antibodies. But after two months, progress stalled. The memory B cells were present in large numbers and expressed potent antibodies, but the antibodies were not getting any stronger. Also, although some of these antibodies were able to neutralize Delta and other variants, there was no overall improvement in breadth.

The researchers found that in convalescent patients, however, memory B cells continued to evolve and improve up to one year after infection. With every memory B cell update, more potent and more broadly neutralising memory antibodies were coming out.

There are several potential reasons that memory B cells produced by natural infection might be expected to outperform those produced by mRNA vaccines, the researchers said.

It is possible that the body responds differently to viruses that enter through the respiratory tract than those that are injected. Or perhaps an intact virus goads the immune system in a way the vaccines’ spike protein antigens simply cannot. It may also be possible that the virus persists in the naturally infected for weeks, giving the body more time to mount a robust response. The vaccine, on the other hand, is flushed out of the body mere days after triggering the desired immune response.

Memory B cells appear to undergo limited bouts of evolution in response to mRNA vaccines, a finding which may have significant implications for booster shots. A booster with the current mRNA vaccine would likely stimulate memory cells to produce antibodies strongly protective against the original virus and somewhat less so against the variants, Prof Nussenzweig said.

“When to administer the booster depends on the object of boosting,” he said. “If the goal is to prevent infection, then boosting will need to be done after 6 to 18 months depending on the immune status of the individual. If the goal is to prevent serious disease, boosting may not be necessary for years.”

Source: Rockefeller University

Categories : COVID T-cellsTags :

Severe COVID May Lead to Stronger Immunity

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Researchers from La Jolla Institute for Immunology (LJI), The University of Liverpool and the University of Southampton have discovered that the degree of COVID severity appears to be linked to how long-lasting and strong the subsequent immunity is. 

“The data from this study suggest people with severe COVID-19 cases may have stronger long-term immunity,” said study co-leader LJI Professor Pandurangan Vijayanand, MD, PhD.

The research examines T-cells from COVID infections in unprecedently high detail.

“This study highlights the enormous variability in how human beings react to a viral challenge,” added co-leader Christian Ottensmeier, MD, PhD, FRCP, a professor at the University of Liverpool and adjunct professor at LJI.

Vijayanand and Ottensmeier have been studying how antibodies and the different subsets of T-cells control COVID disease severity. In this study, they examined CD8+ T-cells, which are the T-cells responsible for destroying virus-infected cells, and “memory” CD8+ T-cells are also important for guarding the body against reinfections of the same virus. These memory T-cells are poised to rapidly proliferate and engage their cell-destroying functions on subsequent antigen encounters. They can reside in peripheral organs and their memory can also be shaped by infection history.

Utilising a new technique called single-cell transcriptomics analysis, they were able to study expressions of individual genes of 80 000 CD8+ T-cells drawn from 39 COVID patients and from 10 non-exposed donors, whose blood samples had been taken before the pandemic. Of the COVID patients, 17 cases were mild and non-hospitalised, 13 were hospitalised and 9 had required ICU care.

Surprisingly, the researchers found that the strongest CD8+ T-cell responses were from those with the more severe form of the disease, and not the milder cases.”There is an inverse link between how poorly T cells work and how bad the infection is,” observed Ottensmeier. “I think that was quite unexpected.” A stronger response would be expected from CD8+ T-cells in mild cases due to having the resources of a better functioning immune system. However, the mild group of CD8+ T-cells showed signs of “exhaustion”, which happens when the immune system overloads the T-cells, causing them to lose effectiveness.

The researchers believe that it will be beneficial to study whether this phenomenon may hinder the ability to build long-term immunity.

“People who have severe disease are likely to end up with a good number of memory cells,” said Vijayanand. “People with milder disease have memory cells, but they seem exhausted and dysfunctional—so they might not be effective for long enough.

“What the researchers would like to look at next is to look at T-cells from lung tissue as opposed to blood samples, because that is where the infection hits hardest.

“This study is very much a first step in understanding the spectrum of immune responses against infectious agents,” said Ottensmeier. The researchers will also look at T-cells in cancer patients who are also infected with COVID.

Source: Medical Xpress

Journal information: Anthony Kusnadi et al, Severely ill COVID-19 patients display impaired exhaustion features in SARS-CoV-2-reactive CD8+ T cells, Science Immunology  21 Jan 2021: Vol. 6, Issue 55, eabe4782 DOI: 10.1126/sciimmunol.abe4782