Immunological memory

Immunological memory is the ability of the immune system to quickly and specifically recognize an antigen that the body has previously encountered and initiate a corresponding immune response. Generally, they are secondary, tertiary and other subsequent immune responses to the same antigen. The adaptive immune system and antigen-specific receptor (e.g., T-cell receptors) generation are responsible for adaptive immune memory. After the inflammatory immune response to danger-associated antigen, some of the antigen-specific T cells and B cells persist in the body and become long-living memory T and B cells. After a second encounter with the same antigen, they recognize the antigen and mount a faster and more robust response. Immunological memory is the basis of vaccination. Emerging resources show that even the innate immune system can initiate a more efficient immune response and pathogen elimination after the previous stimulation with a pathogen, respectively with pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). Innate immune memory (also called trained immunity) is neither antigen-specific nor dependent on gene rearrangement; the different response is caused by changes in epigenetic programming and shifts in immunometabolism. Innate immune memory has been observed in invertebrates and vertebrates. Immune memory can be lost if the corresponding memory cells die out ("immune amnesia"). For example, previously acquired immune memory can be depleted by measles in unvaccinated children, leaving them at risk of infection by other pathogens in the years after infection. This weakening of the immune system increases the risk of death from other diseases.