Table 2. Impact of obesity on the immune system.

Parameter of the immune system	Model	Level of change in the immune system	Resources
Development of leukocyte	HFD-fed mice	↑Myeloid progenitor cells ↓Lymphoid progenitors ↓Thymic output of naive T cells	[72]
	Obese and insulin-resistant patients	↓Thymic output of naive T cells	[72]
	Adipocyte-rich bone marrow in C57BL/6J mice	↓ Hematopoiesis	[77]
	Leptin receptor-deficient mice	↓ Hematopoiesis	[83]
Inflammation of leukocytes	HFD-induced obese mice	↑ T-cell infiltration in adipose	[84]
		↑M1 macrophages
		↓ M2 macrophages in adipose	[85]
		↑ TH1 ↓ Treg cells in adipose	[81,86]
	Obese human subjects	↑ CD4+ T cells ↓ CD8+ peripheral T cells	[87]
		↑ NF-κβ activation in PBMCs	[88]
		↑Migration inhibition factor (MIF), IL-6 ↑ TNF-α ↑ MMP-9 mRNA expression in PBMCs	[88]
	Morbidly obese human subjects	↑ TH1 and ↑ Treg cells	[89]
		↑ CD4+ and CD8+ T-cell proliferation	[89]
Lymph	HFD-induced obese mice	↓ Inguinal lymph node size ↓ T-cell count	[90]
		Impaired lymphatic fluid transport, and dendritic cell migration	[90]
Bone marrow	Obese male and female	Adiposity in bone marrow	[91]
	HFD-fed Wistar rat	↑ Proinflammatory gene expression of mesenchymal stem cells	[92]
Spleen↑	HFD-fed mice	Increased memory T cell ↓ T-cell receptor diversity	[72]
Thymus	HFD-fed mice	↑ Thymic involution and adiposity	[72]
	Leptin deficient (ob/ob mice)	↓ Thymus size and cellularity ↑ Thymocyte apoptosis	[93]
Clinical leukocyte profiles	Weight loss, overweight, and obese subjects	↓WBC count	[94]
Immunity parameters	Diet-induced obese mice	↓ Dendritic cell antigen presentation ↓ Maintenance of influenza-specific CD8+ memory T cells	[95]
	Leptin-deficient (ob/ob) mice	↓ Cell-mediated immunity	[96]
	Diabetic and obese mice	↑ Lung cancer metastasis ↓ NK cell function at early cancer stages	[97]
	Overweight children and child obesity	↑ Tetanus vaccine failure risk	[98,99]
	Obese adults	↑ Risk of influenza vaccine failure ↑ Allergic disease	[100]
	High obesity prevalent in community	↑ Influenza-related hospitalizations	[101]
Inflammatory cytokines and chemokines	Diet-induced obese mice	↓ TGFβ concentration in the lung and ↑ TGFβ concentration in BALF	[102,103]
		↑ TNFα concentration in plasma ↑ mRNA expression in lung ↑ BALF concentration	[103,104]
		↑ G-CSF concentration in lung	[105]
		↓ MIP1α concentration in BALF ↑ MIP1α concentration in lung	[105]
		↓ IL-5 concentration in BALF at the time of infection	[105]
		↑ Leptin concentration in serum ↑ mRNA for Leptin expression in lung	[106,107]
		↓ IL-1β concentration in the lung and ↓ mRNA for IL-1β expression in the lung during influenza infection	[104,105,107]
		↓ mRNA for IL-2 expression in lung	[108]
		↑ IL-6 concentration in serum and lung during infection	[105,108]
		↓ Adiponectin concentration in serum and lung BALF	[103,107]
		↑ Plasma MIP2α concentration	[109]
		↑ MCP-1 concentration in BALF during infection	[110]
		↓ Lung mRNA expression for IFNα and IFNβ	[108]
Immune cell	HFD-induced obese mice	↓ Macrophage migration to the lung ↑ M1 polarization	[110]
		∼ NK cells count in lung	[102,108,110]
	Leptin-deficient OB model mice	↑ Number of alveolar macrophages in BALF	[110,111]
		↑ NK cells count in lung	[102,108,110]
	HFD-induced obese mice	↓ Plasmacytoid dendritic cell count in the lung ↓ Antigen presentation during influenza infection ↓ T-cell proliferation ↓ Lung double negative dendritic cell ↓ pDCs count during infection	[95]
		↑ Neutrophil polarization ↑ Neutrophil net production ↑ BALF infiltration during influenza infection
		↓ Mature bone marrow B cells and cross-reactive H1N1 and PR8 antibodies during influenza infection	[112]
		↓ T-cell count ↑ OCR: ECAR ratios	[112,113]

Here, ↑, increased; ↓, decreased; ∼, unchanged. Abbreviations: BALF, bronchoalveolar lavage fluid; G-CSF, granulocyte-colony stimulating factor; HFD, high-fat diet; IL-2, interleukin-2; IL-5, interleukin-5; IL-6, interleukin-6; MIP1α, macrophage inflammatory protein 1α; MIP2α, macrophage inflammatory protein 2α; MMP-9, matrix metalloproteinase-9; NF-κβ, nuclear factor κ B; NK, natural killer; PBMC, peripheral blood mononuclear cell; pDC, plasmacytoid dendritic cell; PR8, Puerto Rico 8; TGF_β, transforming growth factor-β; T_H1, T-helper cell-1; T_reg, regulatory T cell; WBC, white blood cell.