Vindictive killers
Innate immunity can learn
Kirill Stasevich, Science and Life (nkj.ru ) based on the materials of The Scientist.
We know that immunity is divided into innate and acquired. Many immune cells and molecules are involved in both. Cells and molecules of innate immunity react to some features that are characteristic of a particular class of pathogens as a whole. For example, bacteria in the cell wall have special substances by which it is possible to distinguish a bacterium from a non-bacterium. And many viruses, once in the cell, fill it with special double-stranded RNA molecules, while the viruses themselves may be different, they just have such a common feature.
Cancer cells also have common features. Innate immunity is initially tuned to such distinctive features, and reacts to them quite quickly. But he does not recognize pathogens very accurately, and therefore he cannot always cope with the disease until the end.
To purposefully get rid of a particular nuisance, there is an acquired immunity, which, when faced with a particular pathogen, learns its molecular signs and in the future only hits it. Acquired immunity does not react to bacteria in general, but to a separate species, to some harmful staphylococcus; moreover, the cells of acquired immunity will remember the "visit" of this pathogen into the body, and in the future, if it reappears, such memory cells will quickly turn on the necessary instructions - and the pathogen will disappear before it really harms.
Both immunity, innate and acquired, work together, but previously it was believed that in a certain sense they are separated, that innate differs from acquired by non-specificity and "unconsciousness". However, a few years ago it turned out that some cells of innate immunity – NK, the so–called natural or natural killer - remember the molecular features of pathogens with which they fought, and this memory is formed independently of T- and B-cells related to acquired immunity. Experiments in which memorable natural killers were found were performed on mice, but recently an article appeared in Science Immunology stating that human NK cells have their own memory (Human natural killer cells mediate adaptive immunity to viral antigens).
First, researchers from Baylor College of Medicine took mice with a humanized immune system – this means that the animals' own immune cells were replaced by human ones–and injected some of them with HIV shells. The fight against viruses is the responsibility of natural killers, so they had to respond to the appearance of the immunodeficiency virus, albeit incomplete.
Then NK cells were collected from the body of mice, grown in a laboratory culture and then the immunodeficiency virus, or influenza virus, or some harmless non-viral protein was added to them again. Immune cells taken from mice that were not injected with HIV proteins either reacted poorly or did not react at all to what was then added to their culture. But NK cells taken from mice injected with HIV proteins clearly reacted to the immunodeficiency virus, much weaker to the influenza virus, and did not react at all to an extraneous protein.
That is, despite the fact that NK cells belong to the innate immune system, they have to some extent remembered the viral attack. But there was one peculiarity: they were taken from the liver and spleen, and only those taken from the liver showed memory.
For the next experiment, 40-60-year-old people who had chickenpox in childhood were invited. They were injected with chickenpox virus glycoprotein, after which a swelling formed on the skin at the injection site. In this swelling there were NK cells that reacted specifically to the chickenpox virus, that is, they again demonstrated a memory for the virus, which was preserved in immunity for several decades. But NK cells taken from another place – not from where the viral glycoprotein was injected – did not show any special reaction.
The authors of the work believe that NK cells with memory are also associated with the liver in humans. But why they are associated with the liver and how immune memory appears in the cells of innate immunity in general remains to be seen. Additional immune memory is very important, because it becomes possible to create more effective vaccines that will teach additional groups of "memory" cells.
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