Table 1 Age-related changes to the immune system, adapted from [3]

Innate immunity

Neutrophils

Reduced phagocytic ability of opsonized bacteria and impaired superoxide production

Monocytes or macrophages

Reduced levels of MHC class II complexes, reduced phagocytic ability and impaired superoxide production

Dendritic cells

Impaired capability to phagocytose apoptotic cells; impaired migration

Natural killer cells

Reduced cytotoxicity

Acquired immunity

T cells

Thymus atrophy

Reduced naïve cells leaving thymus, severely contracted T-cell repertoire after 70 years

Impaired expansion and differentiation

Increased proinflammatory cytokine release, reduced IL-2 production

Increased memory and effector cells

Impaired T-cell help of B cells

Reduced regulatory T cells; possible increased inflammation and autoreactivity

Expanded clones of herpes virus (for example, cytomegalovirus) CD8+ cells, dominating the T-cell repertoire and limiting response to other pathogens

B cells

Reduced number of mature B cells leaving bone marrow

Increased memory B cells, decline in naïve B- cells

Reduced responsiveness to stimulatory molecules

Impaired antibody response to vaccination