Immune system aging and the aging-related diseases in the COVID-19 era.

• Aging affects the ability of human immune system to fight infections and neoplasms. • All components of the innate and adaptive immune system are affected. • Major mechanisms of immune system aging are immunosenescence and inflammaging. • Immunosenescence and inflammaging lead to aging-related chronic inflammatory diseases. • Immunosenescence and inflammaging decide about severity of COVID-19. The interest in the process of aging, and specifically in how aging affects the working of our immune system, has recently enormously grown among both specialists (immunologists and gerontologists) and representatives of other disciplines of health sciences. An obvious reason for this interest is the current pandemics of COVID-19, known to affect the elderly more than younger people. In this paper current knowledge about mechanisms and complex facets of human immune system aging is presented, stemming from the knowledge about the working of various parts of the immune system, and leading to understanding of immunological mechanisms of chronic, inflammatory, aging-related diseases and of COVID-19. [ABSTRACT FROM AUTHOR]