. 2021 Nov 23;22(8):484–498. doi: 10.1038/s41577-021-00646-4

Table 1.

Changes in main immune cell populations in ageing

Immune cell population	Age-associated changes	Methods used for analysis
*Mice*
Monocytes	Increased abundance in the spleen and blood^135,136	Flow cytometry
Macrophages	Decreased abundance of alveolar macrophages with reduced proliferative capacity and phagocytosis^25,150,151 Increased abundance of Fn1⁺Ccr2⁺ interstitial macrophages^25,27 Decreased abundance of peritoneal macrophages^25,30 Increased abundance of CX₃CR1⁺ macrophages in the liver²⁵ and kidney¹⁵² Increased abundance of fetal-derived macrophages in mammary tissue²⁸	scRNA-seq, flow cytometry, microscopy
DCs	Decreased abundance of cDC1s in the spleen²⁵ Decreased abundance of cDC2s in the peritoneum²⁵ Decreased abundance of pDCs in the spleen^25,153 and liver²⁵	scRNA-seq, flow cytometry
Neutrophils	Increased abundance in the lungs and liver^25,27	scRNA-seq, flow cytometry
ILCs	Decreased abundance of NK cells in the spleen, peritoneum, lungs and liver²⁵ Increased abundance of NK cells in neurogenic niches⁴⁷ Decreased abundance of ILC1s in the liver²⁵ Decreased abundance of ILC2s in the lungs²⁵ Increased abundance of ILC2s in the brain⁵¹	scRNA-seq, flow cytometry, microscopy
B cells	Increased abundance of age-associated B cells in the spleen and meninges^92,93,96 Increased abundance of plasma B cells in the kidney, adipose tissue and bone marrow^9,26 Accumulation of Apoe⁺ age-associated B cells in the spleen⁵⁷ Accumulation of Zbtb32⁺ age-associated B cells in the spleen²⁵ Increased abundance of Zcwpw1⁺ B1 cells in the peritoneum²⁵	scRNA-seq, flow cytometry
γδ T cells	Increased abundance of Vγ6⁺ cells in lymph nodes⁸² Decreased abundance of Sox4⁺ cells in the spleen²⁵ Increased abundance in the lungs and liver²⁵	scRNA-seq, flow cytometry
CD4⁺ T cells	Decreased abundance of naive cells in the spleen, peritoneum and lungs^25,154 Increased abundance of exhausted-like PD1⁺ cells in the spleen, peritoneum, lungs and liver^25,69 Increased abundance of cytotoxic cells in the spleen⁶⁹ Increased abundance of activated T_reg cells in the spleen^25,69,154 and adipose tissue¹⁵⁵	scRNA-seq, flow cytometry
CD8⁺ T cells	Decreased abundance of naive cells in the spleen, peritoneum and lungs^25,156 Increased abundance in neurogenic niches¹⁵⁷ Increased abundance of virtual memory cells in the spleen, blood and lymph nodes^156,158 Increased abundance of a CD49d⁺ subset in the spleen¹⁵⁹ Accumulation of exhausted-like PD1⁺ cells in the spleen, peritoneum, lungs, liver, kidney, adipose tissue, meninges and blood^25,160	scRNA-seq, flow cytometry
*Humans*
Monocytes	Increased abundance in the blood^25,60,161 Increased abundance of non-classical CD14⁺CD16⁺ cells in the blood¹⁶²	Flow cytometry
DCs	Decreased abundance of pDCs in the blood¹⁶²	Flow cytometry
B cells	Decreased abundance of B1 cells (CD19⁺CD20⁺CD27⁺CD38^low/midCD43⁺) in the blood¹⁶³ Decreased abundance of the ZBTB32⁺ (CD27⁺CD38^low/mid) subset in the blood²⁵	scRNA-seq, flow cytometry
MAIT cells	Decreased abundance in the blood^25,164	scRNA-seq, flow cytometry
γδ T cells	Decreased abundance in the blood¹⁶⁵ Decreased abundance of Vδ2⁺Vγ9⁺ cells in the blood^25,166,167 Decreased abundance of SOX4⁺ cells in the blood²⁵	scRNA-seq, flow cytometry
CD4⁺ T cells	Decreased abundance of naive cells in the blood^{60,61,137,138} Increased abundance of T_EM cells in the blood¹³⁸ Decreased abundance of recent thymic emigrants in the blood¹³⁷ Decreased abundance of an interferon-activated subset in the blood²⁵ Increased abundance of the cytotoxic subset in the blood (supercentenarians)⁷²	scRNA-seq, flow cytometry
CD8⁺ T cells	Decreased abundance of naive cells in the blood^25,61,138 Increased abundance of T_EM cells in the blood^25,138 Increased abundance of the GZMK⁺(CD28⁺CD57^–) subset of T_EM cells in the blood²⁵ Increased abundance of the CD57⁺ subset in the blood¹⁴⁹	scRNA-seq, flow cytometry, mass cytometry

cDC1, conventional type 1 dendritic cell; cDC2, conventional type 2 dendritic cell; CX₃CR1, CX₃C chemokine receptor 1; DC, dendritic cell; GZMK, granzyme K; ILC, innate lymphoid cell; ILC1, group 1 innate lymphoid cell; ILC2, group 2 innate lymphoid cell; MAIT cells, mucosal associated invariant T cells; NK, natural killer; pDC, plasmacytoid dendritic cell; scRNA-seq, single-cell RNA sequencing; T_EM cell, effector memory T cell; T_reg cell, regulatory T cell.