The Impact of Immunosenescence and Senescence of Immune Cells on Responses to Infection and Vaccination

The innate and adaptive immune systems undergo characteristic changes with age, which contribute to increased incidence, morbidity and mortality of infections and reduced immunogenicity and clinical efficacy of many vaccines in older individuals. Innate immune dendritic cells and macrophages play a crucial role in sensing and initiating immune response to pathogens and vaccines. These cells bridge the innate and adaptive immune responses by virtue of antigen presentation to T cells. Surface markers and cytokine secretion by these cells coordinates the nature of downstream T and B cell responses. T cells play an important role in the network of immune responses to pathogens and vaccines. CD4+ T helper cells enhance and orchestrate innate immune responses. Their interaction with B cells in germinal centers are crucial for antibody responses, which provide long-term protection. Cytotoxic CD8+ T cells directly attack infected and tumor cells and regulatory T and B cells fine-tune the delicate balance of immunological processes.

The impact of age is evident for all cell types of the immune system. Innate immune cells display changes that impair their response to infection and vaccines. Antigen, sensing, presentation and responses are all altered with age. Aging affects individual T and B cells throughout their life-cycle from alterations in hematopoiesis, maturation and homeostasis, to memory generation and effector functions as well as their interactions with other cell types, and the composition and repertoire of the adaptive immune cell compartments.

It is of importance to investigate aging immune cells in different tissue compartments, as a large fraction of these cells reside in distinct lymphoid and non-lymphoid tissues and to consider extrinsic factors (e.g. chronic infection, obesity…) which can influence aging of immune cells. The functions of innate and adaptive immune cells are influenced by the tissue microenvironment. Highly differentiated (or aged) adaptive immune cells can be considered senescent as they share some but probably not all characteristics of classic replicative senescence and they have been suggested as targets for interventions to improve immune function in old age. It is essential to base the design of improved and novel vaccines for older adults on our knowledge of the aged immune system and to include older adults in the clinical development of vaccines and adjuvants.

This Research Topics collects contributions that add to our knowledge on the immune system in old age and the impact of immunosenescence and senescent immune cells on immune responses to infection and vaccination. In addition, it calls for manuscripts discussing approaches to improve immune responses and particularly vaccine-induced immunity in the older population.