巨噬细胞在吞噬凋亡细胞过程中产生TGF-β

It is estimated that more than 500 different species of bacteria, amounting to approximately 1014 cells,
live in the mammalian gut

commensal organisms
FoxP3+ regulatory T cells

TH17 cells
TH17 cells produce IL-17 and IL-22 which induce the expression of proteins important for barrier function, such as mucins and β-defensins
Secondary lymphoid tissue in gut wall

Peyer’s patch

isolated follicles (colon Appendix)

Mesenteric lymph node Diffusely distributed immune cells Lamina propria lymphocyte, LPL intraepithelial lymphocyte, IEL
FoxP3+ Treg
Treg are thought to suppress immune responses by several mechanisms. Of these, the dominant mechanism in the gut seems to be production of the immunosuppressive cytokine IL-10.

IgM Poly-IgR
IgG neonatal Fc receptor (FcRn) bidirectional transport
阻断微生物黏附于黏膜，使多数共生菌滞留于肠 腔而不侵入人体，维持机体和共生菌之间的生态 平衡
与IgG协同，抵御穿越肠道上皮组织的致病菌，控 制感染蔓延
IgA is produced in larger amounts than any other antibody isotype

2 g of IgA per day
T-dependent mechanisms T-independent mechanisms
Transport of IgM and IgG
features of gastrointestinal adaptiveimmunity
The major form of adaptive immunity in the gut is humoral immunity
The dominant protective cell-mediated immune response consists of TH17 effector cells
effector DCs CD11b+CX3CR1+ induce T cells into IFN-γ– or IL-17–producing effector
cells regulatory DCs CD103+CX3CR1− induce the differentiation of naive T cells into
most of the intraepithelial T cells are CD8+ cells
Lamina propria T cells are mostly CD4+, and most have the phenotype of activated effector or memory T cells
T cells within Peyer’s patches and in other follicles adjacent to the intestinal epithelium include CD4+ helper T cells and regulatory T cells
DCs of gastrointestinal immune system
lymphoid follicles, with germinal centers containing B lymphocytes, follicular helper T cells, follicular dendritic cells (FDCs), and macrophages
M cells （microfold cell ） The main function of M cells is transcellular transport of
转铁蛋白
溶菌酶
Defensin

α-defensins(small bowel Paneth cells )


β-defensins (colonabsorptive epithelial cells)
commensal organisms
作用：阻止病原体在肠道的定居

与病原体竞争空间和营养
gut-homing of IgA-producing cells and effector T cells
Effector lymphocytes that are generated in the GALT and mesenteric lymph nodes are imprinted with selective integrin- and chemokine receptor–dependent gut-homing properties, and they circulate from the blood back into the lamina propria of the gut
various substances from the lumen of the intestine across the epithelial barrier to underlying antigenpresenting cells
Antigen-sampling DCs
they extend dendrites through the junctions between adjacent epithelial cells，these DCs are capable of processing and presenting protein antigens to T cells within the GALT
Fc receptor–mediated pathways neonatal Fcγ receptor (FcRn）
Mesenteric lymph nodes（肠系膜淋巴结）
100 to 150 differentiation of B cells into dimeric IgA–secreting
The adaptive immune system in the gut must continuously suppress potential immune responses to food antigens and commensal microbial antigens
Peyer’s patches and isolated follicles
cytokines maintaining homeostasis in the gut immune system
plasma cells and the development of effector T cells as well as regulatory T cells
The cells that differentiate in the mesenteric lymph nodes in response to bowel wall invasion by pathogens or commensals often home to the lamina propria

mucosal immune system

主要包括呼吸道、消化道及泌尿生殖道黏膜固有层和上皮 细胞下散在的无被膜淋巴组织，以及某些带有生发中心、
器官化的（有被膜的）淋巴组织（如扁桃体、小肠的集合 淋巴结、阑尾等）
源自文库
gastrointestinal associated lymphoid tissue bronchopulmonary associated lymphoid tissue genitourinary associated lymphoid tissue
TH2 responses
which are effective in eliminating the worms in intestinal helminthic infections because the TH2 cytokines IL-4 and IL-13 cooperate in enhancing fluid and mucus secretions and inducing smooth muscle contraction and bowel motility
two remarkable properties of gastrointestinal tract
the combined mucosa of the small and large bowel has a total surface area of more than 200 m2

primary or central lymphoid organs
bone marrow B cells thymus T cells
secondary or peripheral lymphoid organs
lymph nodes spleen

cutaneous immune system

产生抗菌物质（如蛋白样毒素）
TLRs and NLRs 的表达对黏膜固有免疫的影响
DCs and macrophages in the lamina propria of the gut inhibit inflammation

IL-10

transforming growth factor-β (TGF-β)
production of secretory IgA in the GALT
secretory immunity：Within the lumen, IgA,
IgG, and IgM antibodies bind to microbes and toxins and neutralize them by preventing their binding to receptors on host cells.

noncommensal pathogenic organisms
physical barrier
epithelial cells barrier mucous barrier secreted mucins 300 to 700 μm membrane-bound mucins 30 to 500 nm 其主要功能： 阻挡微生物接近上皮细胞 为共生菌提供栖息地和营养 捕获并排除病原体 作为分泌型IgA的储存库
中和作用
T cells are found within the gut epithelial layer, scattered throughout the lamina propria and submucosa, and within Peyer’s patches and other organized collections of follicles