you can see a brief of gastrointestinal immunology from Abulabbas book.

1. IMMUNITY INTHE
GASTROINTESTINAL
SYSTEM
Abul K. Abbas, Andrew H. H. Lichtman, Shiv Pillai - Cellular and Molecular Immunology (2014,
Saunders)

2. The gastrointestinal immune system

3. Innate Immunity in the Gastrointestinal Tract
• Intestinal epithelial cells lining the small and large bowel are an
integral part of the gastrointestinal innate immune system,
involved in responses to pathogens, tolerance to commensal
organisms, and antigen sampling for delivery to the adaptive
immune system in the gut
• Several different extensively glycosylated proteins, called mucins,
form a viscous physical barrier that prevents microbes from
contacting the cells of the gastrointestinal tract.

4. Innate Immunity in the Gastrointestinal Tract
• The mucous barrier of the intestine undergoes turnover and
chemical changes in response to various environmental and
immune signals, which allows rapid increases in mucosal barrier
function.
• Defensins produced by intestinal epithelial cells provide innate
immune protection against luminal bacteria, and defects in their
production are associated with bacterial invasion and
inflammatory bowel disease

5. Innate Immunity in the Gastrointestinal Tract
• Toll-like receptors (TLRs) and cytoplasmic NOD-like receptors
(NLRs) expressed by intestinal epithelial cells promote immune
responses to invasive pathogens but also limit inflammatory
responses to commensal bacteria
• In healthy individuals, dendritic cells and macrophages in the
lamina propria of the gut inhibit inflammation and serve to
maintain homeostasis
• Innate lymphoid cells that produce IL-17 and IL-22 are found
mainly in the intestinal mucosa and contribute to immune defense
against some bacteria as well as to mucosal epithelial barrier
function

7. Adaptive Immunity in the Gastrointestinal
Tract
• The major form of adaptive immunity in the gut is humoral
immunity directed at microbes in the lumen
• The dominant protective cell-mediated immune response consists
of TH17 effector cells
• A major mechanism for controlling responses in the gut is the
activation of regulatory T cells (Treg).

8. The Functional Anatomy of the Adaptive
Immune System in the Gastrointestinal Tract
• Adaptive immune responses in the gut are initiated in discretely
organized collections of lymphocytes and antigen-presenting cells
closely associated with the mucosal epithelial lining of the bowel
and in mesenteric lymph nodes
• A major pathway of antigen delivery from the lumen to the GALT is
through specialized cells within the gut epithelium called
microfold (M) cells

10. • Microbial antigens in the gut lumen can be sampled by lamina
propria dendritic cells that extend cytoplasmic processes between
the intestinal epithelial cells
• Mesenteric lymph nodes collect lymph-borne antigens from the
small and large intestines and are sites of differentiation of
effector and regulatory lymphocytes that home back to the lamina
propria.
• Lingual and palatine tonsils are nonencapsulated lymphoid
structures located beneath stratified squamous epithelial mucosa
in the base of the tongue and oropharynx, respectively, and are
sites of immune responses to microbes in the oral cavity.

12. • The gut-homing phenotype of IgA-producing B cells and effector T
cells is imprinted by dendritic cells through the action of retinoic
acid during the process of T cell activation
• The lamina propria contains diffusely distributed effector
lymphocytes, dendritic cells, and macrophages and is the site of
the effector phase of gastrointestinal adaptive immune responses

13. Humoral Immunity in the Gastrointestinal
Tract
• The major function of humoral immunity in the gastrointestinal
tract is to neutralize luminal microbes, and this function is
mediated mainly by IgA produced in the GALT and transported
across the mucosal epithelium into the lumen.
• IgA is produced in larger amounts than any other antibody isotype
• The dominance of IgA production by intestinal plasma cells is due
in part to selective induction of IgA isotype switching in B cells in
GALT and mesenteric lymph nodes.

14. • Secreted IgA is transported through epithelial cells into the intestinal
lumen by an IgA/IgM-specific Fc receptor called the poly-Ig receptor
• The high level of IgA production by intestinal plasma cells is enhanced by
selective gut-homing properties of IgA-producing cells that arise in GALT
and mesenteric lymph nodes
• IgA produced in lymphoid tissues in the mammary gland is secreted into
colostrum and mature breast milk through poly-Ig receptor–mediated
transcytosis and mediates passive mucosal immunity in breast-fed
children.
• FIGURE

18. T Cell–Mediated Immunity in the
Gastrointestinal Tract
• 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
• Dendritic cells and macrophages are abundant in the
gastrointestinal immune system and can participate in stimulating
protective effector T cell responses or inducing regulatory T cell
responses that suppress immunity to ingested antigens and
commensal organisms

19. T Cell–Mediated Immunity in the
Gastrointestinal Tract
• In the gastrointestinal tract, different subsets of effector CD4+ T
cells are induced by and protect against different microbial
species.

20. Regulation of Immunity in the Gastrointestinal
Tract by Regulatory T Cells and Cytokines
• Several cytokines, including TGF-β, IL-10, and IL-2, appear to play
crucial roles in maintaining homeostasis in the gut immune
system, and deficiencies in these cytokines or their receptors
result in pathologic bowel inflammation

21. Oral Tolerance and Oral Vaccines
• Oral tolerance is systemic adaptive immune tolerance to antigens
that are ingested or otherwise administered orally.
• Oral administration of antigen in the setting of concomitant
stimulation of innate immunity can lead to productive adaptive
immune responses, as in the use of oral viral vaccines to induce
protective antibody responses to viruses

22. The Role of the Commensal Microbiome in
Immune Regulation
• Commensal organisms in the intestines are required for and
regulate innate immune responses in the gut, and also influence
systemic innate immunity
• Intestinal commensal organisms influence local and systemic
adaptive immune responses

23. Diseases Related to Immune Responses in the
Gut
• Inflammatory Bowel Disease
• Celiac Disease