Killers without intermediaries
Scientists have found out how immunity works against respiratory viruses
American scientists have found that T-lymphocytes in the lungs, responsible for long-term immunity against respiratory viruses, can be activated more easily than previously thought. According to the authors, this will help in the development of universal vaccines against influenza and the new coronavirus. The results of the study are published in the Journal of Experimental Medicine (Low et al., Tissue-resident memory T cell reactivation by diverse antigen-presenting cells imparts distinct functional responses).
T-lymphocytes, or T-cells, play an important role in the formation of immunity to infections. Memory T cells store information about previously active antigens and form a rapid secondary immune response, destroying the pathogen. Therefore, they are also called killer T cells. The formation of stable immunity with the help of memory T-cells is the basis of the vaccination concept.
But in order for the killer cells located in the lymph nodes to start acting, they need to be targeted - to let them know that the virus is in the body, like a dog, before being released to search for a criminal, they are given to smell him. This function is performed by dendritic messenger cells that deliver fragments of the virus to the memory T-cell.
In addition to lymphoid organs, T cells are also found in other organs, in particular in the lungs. It is these resident immune cells that are activated primarily in the case of recurrent respiratory infections such as influenza or COVID-19. But the mechanisms of their action have not been studied before.
Researchers from the Salk Institute for Biological Research and Yale University decided to find out how these immune cells target the antigen.
"There are long-lived killer T cells inside the lungs that recognize certain viruses and protect against re-infection," the press release says. The words of the head of the study, Professor Susan Kaech, Director of the Center for Immunobiology and Microbial Pathogenesis, Salk Institute. "Studying them will also help us understand how long–term immunity is formed in relation to coronavirus."
The authors suggested that even in this case, dendritic cells would be required to reactivate T-killers to fight a repeated viral attack. However, it turned out that this is not the case. When dendritic cells were removed during an experiment on mice, memory T cells in the lungs in the presence of the influenza virus continued to remain active. For comparison, T-killers in lymph nodes without targeting by dendritic cells did not work.
"At first, our results were disappointing – the memory T-killers continued to recognize the virus after deleting various types of messengers," says the first author of the article, Jun Siong Low, about the experiment. – We soon realized that resident memory T cells are special. They can “see” a repeated flu infection at once through many different messenger cells, including lung epithelial cells. It's an amazing, exciting discovery."
The results showed that the method of reactivation of T cells depends on their anatomical location. In particular, lung resident T cells can be rapidly reactivated by almost any cells at the site of pathogen penetration.
According to the authors, this casts doubt on the existing dogma that memory T cells always require dendritic cells for reactivation, and allows us to hope for the appearance of a universal vaccine against all respiratory viruses over time.
"We will transfer this knowledge to our next study, in which we will look at whether memory T cells are formed in the lungs after coronavirus infection and whether they can protect against re-infection," says Kayech.
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