User:Radka Císařová

= Trained immunity = Trained immunity is relatively new term, which relate to immunological memory in innate immune system. Immunological memory had been always considered a part only of adaptive immunity however there is a growing pool of evidence regarding immunological memory in the innate part of immune system; also called the innate immune memory. There is no development of specific antibodies in the innate immunity like it is in the adaptive part, but there can be certain training of immune cells for secondary encounter with the pathogen. Training of innate immunity is mediated mostly by epigenetic modifications, lasts maximaly for several months in contrast with the classical immunological memory and is usually unspecific because there is no production of specific antibodies/receptors.

Innate immune memory is a term used sometimes when refering to innate immunity across all taxons and when speaking about a certain group of organisms, there can be used more specific term, and sometimes it is used as a synonym to trained immunity. The term trained immunity refers only to innate immune memory of vertebrates.

Proofs of trained immunity are found maily at NK cells and monocytes/macrophages, less at γδ T cells and innate lymphoid cells.

Monocytes and macrophages
Monocytes/macrophages can undergo epigenetic modifications after a ligation of their pattern recognition receptors (PRRs), which prepare these cells to the secondary encounter with the pathogen. The secondary response does not have to be hightened only against the same pathogen but also against different pathogens, whose antigens are recognised by the same PRRs. This effect has been discibed several times when stimulating cells by β-glucan, Candida Albicans or vaccination against tuberculosis with a vaccine containing BCG. Monocytes are very short lived cells however the hightend secondary response can be spotted even several months after the primaly stimulation. This indicates that the immune memory is created at the level of progenitor cells but we do not know how this is achived so far.

NK cells
The trained immunity at NK cells looks more like classic immunological memory because there is a development of at least partially specific clones of NK cells. These cells have receptors on there surface against certain antigents, with which they came to contact during the first stimulation. After the encounter with cytomegalovirus certain clones of NK cells, which have a Ly49H receptor on their surface, expand and then this population shows signs of immunological memory.