Abstract
Owing to its memory and plasticity, the immune system (IS) is capable of recording all the immunological experiences and stimuli it was exposed to. The combination of type, dose, intensity, and temporal sequence of antigenic stimuli that each individual is exposed to has been named “immunobiography.” This immunological history induces a lifelong continuous adaptation of the IS, which is responsible for the capability to mount strong, weak or no response to specific antigens, thus determining the large heterogeneity of immunological responses. In the last years, it is becoming clear that memory is not solely a feature of adaptive immunity, as it has been observed that also innate immune cells are provided with a sort of memory, dubbed “trained immunity.” In this review, we discuss the main characteristics of trained immunity as a possible contributor to inflammaging within the perspective of immunobiography, with particular attention to the phenotypic changes of the cell populations known to be involved in trained immunity. In conclusion, immunobiography emerges as a pervasive and comprehensive concept that could help in understanding and interpret the individual heterogeneity of immune responses (to infections and vaccinations) that becomes particularly evident at old age and could affect immunosenescence and inflammaging.
Highlights
THE IMMUNE SYSTEM (IS) AS A COMPLEX SYSTEMLife is a continuous exposure to a large variety of threatening and potentially damaging agents collectively indicated as stressors, which can be divided into two basic categories: external and internal stressors
Trained immunity entails a cross-protection from different pathogens, and the first antigenic contact appears to be important in determining what kind of protection will be evoked
We have recently proposed that an age-related increase in the production of danger-associated molecular patterns (DAMPs) can impinge upon the level of inflammaging more importantly than pathogen-associated molecular patterns (PAMPs), through innate immune cells receptors, leading to innate inflammatory response [1]
Summary
Life is a continuous exposure to a large variety of threatening and potentially damaging agents collectively indicated as stressors, which can be divided into two basic categories: external and internal stressors. The IS is composed of cells and receptors devoted to the recognition of, and response to antigenic stressors, and is considered a paradigmatic example of complex system As such, it is characterized by specific features, such as degeneracy (the capability of a single receptor to recognize a variety of molecular patterns); networking (the capability of IS cells to interact and cross-talk with each other); plasticity (the capability to adapt to different situations); and the socalled bow tie architecture has been conceptualized to integrate all these characteristics of the IS. The same concept is valid for all the responses of the IS as a whole The combination of these elements (type, intensity, and temporal sequence of antigens) is called “immunological biography” or immunobiography, and it can be considered unique for each individual. We will use the concept of immunobiography as a fil rouge of this review
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