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

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: 59-67 (2003)

© 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

Tight junctions maintain mucosal integrity

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”

The “Common Mucosal Immune System”

“D-MALT” “O-MALT”

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

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.

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

Nature Reviews Immunology Nagler-Anderson Vol 1: 59-67 (2003)

(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: 59-67 (2003)

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.

Activation induced cytidine deaminase Fagarasan and Honjo; Nature Reviews Immunology: 3: 63-72 (2003)

Reciprocal down-regulation

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.

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

Selectins and integrins bind to tissue specific cellular addressins (like zip codes). Brandtzaeg et al. Immunology Today: 20:267-277 (1999)

Differential lymphocyte trafficking Brandtzaeg et al. Immunology Today: 20:267-277 (1999)

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

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

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

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

The Nasal Associated Lymphoid Tissues (NALT)

Recognition of commensals and pathogens - TLRs Basolateral expression

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

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.

Th0 www.scielo.br/scielo.php?pid=S0100-879X200900... Also Tr1 and Th3

Artis, 2008 Artis, 2008 1014

Artis, 2008

Artis, 2008

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

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. http://nutrition.about.com/od/therapeuticnutrition1/p/pro_prebiotics.htm