Table 3.

Alterations in the innate and adaptive immune system of infants and older adults

Cell	Changes in healthy older adults	Changes seen in healthy infants
Neutrophils	Increased incidence of neutropenia32 Altered cytokine production34 Impaired migration33 Reduced pathogen killing35 Increased apoptosis38	Reduced migratory ability55 Reduced degranulation57 Preserved phagocytosis88 Reduced NET generation60 Preserved ROS generation53
Macrophage/ monocytes	Reduced phagocytosis and production of free radicals89 Possible reduced efferocytosis90 Decreased ability to antigen present due to reduced expression of MHC class II91	Reduced ability to secrete inflammatory mediators after LPS stimulation92
Dendritic cells	Relative frequency controversial93 DC function maintained in healthy older adults94 but impaired in frail older adults95	Negative correlation between the number of plasmacytoid DC and age
NK cells	Increased numbers but reduced cytotoxicity96	Reduced cytotoxicity97 NK cells from children are phenotypically different from adults in terms of cell surface receptors.98
Adaptive Immunity	Reduced numbers of naïve T cells T cell exhaustion Decreased capacity to respond to novel antigens Lower affinity antibodies Reduced numbers of B cells99	Increased Tregs Blunted humoral responses97

Table 3 gives an overview of cellular features of changing features of immunity in humans with ages. Features in neutrophils are expanded on later in the text.

DC, dendritic cell; LPS, Lipopolysaccaride; MHC, major histocompatibility complex; NET, neutrophil extracellular trap; NK, natural killer; ROS, reactive oxygen species; Treg, T regulatory lymphocyte.