Population immunology: Germs, aging and inflammation

Immunosenescence has been described as a combination of dysfunctional immunity with a state of low grade chronic inflammation (inflammaging) in the elderly. These processes may result either in increased susceptibility to infections or in the development of chronic inflammatory diseases and frailty in the elderly. However, not all elderly bear a dysfunctional immunity. Senescence may also be accompanied by a remodeling of the immune system that is associated with increased longevity and healthy aging. The concept of healthy aging has been proposed initially in Europe to describe the individuals who reach advanced age free of inflammatory consequences of immunosenescence. Since then, the quest for biological markers of healthy aging has been focused on the consequences of inflammaging, but this inflammatory status might be a deleterious event restricted to populations living in clean environments. In other parts of the world where infectious diseases are still prevalent, inflammatory responses may be beneficial and needed to cope with infections agents. Therefore, the debate over the biological markers of healthy aging would have to take into account geographical, cultural and environmental differences that reflect the changes in the past century in our contacts with microorganisms and their immunological consequences.