Immunosenescence and infectious diseases

In this chapter, we will briefly review the principal modes of interactions taking place between the host’s immune system and the principal groups of microorganisms. We will focus on the way these modes of interactions are modified by intrinsic and extrinsic factors associated with ageing. As described in Chapter 45, one of the principal features of immunosenescence is linked to thymus involution with subsequent loss of diversity of the repertoire of naïve T-cells. This has a major impact on the adaptative immune responses developed against newly encountered pathogens. Interestingly, more ubiquitous mechanisms associated with the ageing process itself could also have an impact on innate immunity. Defective autophagy impairs the clearance of intracellular pathogens and age-related defects of the ubiquitination-proteasome pathway concur to blunt antiviral responses. In summary, healthy ageing is associated with subtle impairments of innate and adaptive immunity directed against all groups of pathogens. The presence of comorbid states often exerts a synergistic effect on the susceptibility to infectious diseases.