1. Microbial Conditioning of the
Mucosal Immune System
Silbart Lecture – 2/19/14

2. Surface Areas: Skin – 2 m2 Lung – 140 m2 G.I. – 200 m2
Pathogens/toxins often enter our bodies across mucosal surfaces
Surface Areas:
Skin – 2 m2
Lung – 140 m2
G.I. – 200 m2
Thus, a very large
commitment of lymphocytes is needed to protect these surfaces
Nature Reviews Immunology
Nagler-Anderson Vol 1: (2003)

9. © 2003 by LIPPINCOTT WILLIAMS & WILKINS Fundamental Immunology
                                                                                     
Innate and antibody-mediated mucosal host defense mechanisms. Shown are soluble antimicrobial proteins lactoperoxidase, lactoferrin, and lysozyme, and the peptide defensins. Human neutrophil peptide (HNP) and Paneth cells in crypt regions produce a-defensins, whereas epithelial cells secrete b-defensins.
Anti-microbial peptides (AMPs)
© 2003 by LIPPINCOTT WILLIAMS & WILKINS Fundamental Immunology

11. Tight junctions maintain mucosal integrity

12. Fundamentals of Mucosal Immunology
Presence of foreign antigens at a mucosal surface is generally not sufficient to elicit a mucosal immune response - in fact, in the absence of “signal 1 - danger” Ag is often toleragenic (e.g. non-replicating protein antigens).
Regulation of mucosal immune responses is distinct from systemic “humoral” immunity
Stimulation at one mucosal surface often results in mucosal immunity at many, if not all mucosae - “CMIS”

13. The “Common Mucosal Immune System”

15. “D-MALT”
“O-MALT”

19. Cross section of a Peyer’s Patch; epithelial cells (blue) T cells (red) B cells (green)

20. Separate Inductive and Effector Sites
Antigen uptake occurs at the “follicle associated epithelium” (FAE), a lymphoepithelial structure that has few if any goblet cells (thereby less mucus) and specialized epithelial cells known as “M” cells.
M cells sample the intestinal surface and lumen through phagocytosis, then pass antigens into a sub-epithelial pocket without processing.
Note: Many pathogens exploit Peyer’s patches - e.g. Salmonella sp.

24. Fagarasan and Honjo; Nature Reviews Immunology: 3: 63-72 (2003)

28. Nature Reviews Immunology
Nagler-Anderson Vol 1: (2003)

29. (DC’s – red, bacteria green)
Entry of GFP- labeled Salmonella typhimurium through the FAE, and uptake by CD11c+ DCs
(DC’s – red, bacteria green)
Nature Reviews Immunology
Nagler-Anderson Vol 1: (2003)

30. The Germinal Center Microenvironment
In the dome region of a Peyer’s patch, the T helper cell population is heavily biased toward a Th2 response.
This leads to B cell isotype switching from sIgM+/sIgD+ to sIgA, heavily influenced by TGF-beta and IL-5.

31. Activation induced cytidine deaminase
Fagarasan and Honjo; Nature
Reviews Immunology: 3: (2003)

32. Reciprocal down-regulation

33. Lymphocyte trafficking
Antigen-specific, IgA-committed lymphoblasts emigrate from the FAE, lodge transiently in the mesenteric lymph nodes, where antigen re-exposure and secondary rounds of proliferation/differentiation can occur.
These cells rejoin circulation via the thoracic duct, then home to effector tissues, generally the lamina propria of the intestine or lung, or a variety of glandular tissues.

36. Kunkel and Butcher Nature Reviews Immunology 3: 822-829 (2003)

38. Selectins and integrins bind to tissue specific cellular addressins (like zip codes).
Brandtzaeg et al. Immunology Today: 20: (1999)

39. Differential lymphocyte trafficking
Brandtzaeg et al. Immunology Today: 20: (1999)

40. Kunkel and Butcher; Nature Reviews Immunology 3: 822-829 (2003)

41. Secretory IgA Production
Once the IgA-committed lymphoblasts extravasate into the lamina propria, they will proliferate in the presence of antigen, then terminally differentiate into an S-IgA secreting plasma cell.
S-IgA dimers, joined by a “J” chain, bind to the polymeric immunoglobulin receptor (pIgR), and S-IgA is expelled into the lumen with the secretory component attached.
Note: S-IgA is substantially more proteolytically stable than IgG

42. Trans-epithelial transport of dimeric IgA
© 2003 by LIPPINCOTT WILLIAMS & WILKINS Fundamental Immunology

44. Secretory component derived from pIgR (22% sugar)
Molecular dimensions, proteolytic fragments, and domain structure of the human dimeric secretory immunoglobulin A1 molecule.
© 2003 by LIPPINCOTT WILLIAMS & WILKINS Fundamental Immunology

47. The Nasal Associated Lymphoid Tissues (NALT)

50. Recognition of commensals and pathogens - TLRs
Basolateral expression

52. Defects in NOD2 are found in 30% of Crohn’s disease patients

58. Tolerance
Mediated by encounter with antigen while T cells are immature, usually within the thymic epithelium
Secondary mechanisms for peripheral tolerance through anergy or apoptosis.
“high-zone” tolerance occurs following activation induce apoptosis.
Tolerance is a dynamic process, and depends on dose, timing, route of infection and localization of antigen.

62. Th0
Also Tr1 and Th3

63. Artis, 2008
Artis, 2008
1014

64. Artis, 2008

65. Artis, 2008

70. Commensals required for proper development as neonates
Premature birth C-sections
Antibiotic use
C. diff necrotizing enterocolitis (NEC)
[colonization resistance]
Bifidobacter and Lactobacillus love breastmilk oligo-saccharides

71. Intestinal dysbiosis, pre-biotics and probiotics
Prebiotics are non-digestible carbohydrates, such as oligosaccharides and fructo-oligosaccharides. They remain in the digestive tract where they stimulate the growth of beneficial bacteria.