Gastrointestinal Defense Mechanisms

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Gastrointestinal Defense Mechanisms

• Acidity in the stomach limits the number of
  viable microbes that gain access the small
  intestine

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Gastrointestinal Defense Mechanisms

• Acidity in the stomach limits the number of
  viable microbes that gain access the small
  intestine
• Non-immunologic defense mechanisms
• Intestinal biliary secretions (some microbes
  sensitive)
• Proteolytic enzymes can degrade bacterial cell
  walls

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Gastrointestinal Defense Mechanisms

• Epithelium serves as a barrier with tight
  junctions between individual enterocytes forming
  an epithelial monolayer that prevents the passage
  of large molecules

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Gastrointestinal Defense Mechanisms

• Epithelium serves as a barrier with tight
  junctions between individual enterocytes forming
  an epithelial monolayer that prevents the passage
  of large molecules
• Enterocytes on villi are replenished every 3 to 6
  hours, this minimizes the opportunity for
  successful colonization by potential pathogens

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Gastrointestinal Defense Mechanisms

• Colonization resistance is the ability of
  normal microbes to inhibit the colonization of
  invading microbes in the intestine

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Gastrointestinal Defense Mechanisms

• Colonization resistance is the ability of
  normal microbes to inhibit the colonization of
  invading microbes in the intestine
• Inhospitable pH, nutrient competition,
  competition for attachment sites, local
  production of antibiotics called bacteriocins

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Gastrointestinal Defense Mechanisms

• Colonization resistance is the ability of
  normal microbes to inhibit the colonization of
  invading microbes in the intestine
• Inhospitable pH, nutrient competition,
  competition for attachment sites, local
  production of antibiotics called bacteriocins
• Microhabitat communities are characteristic of a
  species and to some extent the nutrition and
  environment of the animal

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Gastrointestinal Defense Mechanisms

• Germfree rodents (without normal gut bacteria),
  all the immunologically important organs
  (including intestine) are underdeveloped

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Gastrointestinal Defense Mechanisms

• Germfree rodents (without normal gut bacteria),
  all the immunologically important organs
  (including intestine) are underdeveloped
• Direct fed microbials enhance immunity and growth
  in young pigs

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Mucosal Immunology
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Mucosal Immunity Pig Intestine

• Antibodies in colostrum provide the source of
  immune protection for newborn pigs

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Mucosal Immunity Pig Intestine

• Antibodies in colostrum provide the source of
  immune protection for newborn pigs
• Maximum immunoglobulin absorption occurs 4-12
  hours after initial suckling and then declines
  rapidly due to gut closure

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Mucosal Immunity Pig Intestine

• Antibodies in colostrum provide the source of
  immune protection for newborn pigs
• Maximum immunoglobulin absorption occurs 4-12
  hours after initial suckling and then declines
  rapidly due to gut closure
• During this time, colostrum immunoglobulins are
  absorbed across the intestinal epithelium and
  into lymphatic vessels

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Mucosal Immunity Pig Intestine

• Serum antibodies have been detected as early as 3
  hours after birth and can be similar to those of
  the sow within 24 hours after birth.

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Mucosal Immunity Pig Intestine

• Serum antibodies have been detected as early as 3
  hours after birth and can be similar to those of
  the sow within 24 hours after birth.
• The initial antibody profile acquired via
  colostrum is restricted to antigens to which the
  sow has been exposed

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Mucosal Immunity Pig Intestine

• Predominant immunoglobulin in colostrum is IgG
  and while maternal IgG will protect against
  systemic pathogens, pathogenic agents are
  encountered at mucosal surfaces where IgG
  antibodies are rarely found

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GUT ASSOCIATED LYMPHOID TISSUE(GALT)

• One of the major subdivisions of the immune
  system
• 25 of intestinal mucosa is lymphoid tissue

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GALT

• Major lymphoid compartments
• Lymphocytes are present between intestinal
  epithelial cells lining the intesintal villus
• Organized lymphoid follicles (Peyers patches)
• Scattered individual or small aggregates of
  lymphoid follicles

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Mucosal uptake of bacteria

• M cells are found in the epithelium overlaying
  Peyers patches

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Characteristic features of MALT
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M cells facilitate antigen uptake.
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M cells

• Originate from epithelial cells that are induced
  to differentiate, contain few lysozomes and low
  levels of phosphatase

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M cells

• Originate from epithelial cells that are induced
  to differentiate, contain few lysozomes and low
  levels of phosphatase
• Serve as a channel for entry of molecules into
  the underlying mucosal follicular region

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M cells

• Originate from epithelial cells that are induced
  to differentiate, contain few lysozomes and low
  levels of phosphatase
• Serve as a channel for entry of molecules into
  the underlying mucosal follicular region
• Bacterial binding to M cells may be favored to
  binding to other epithelial cells, (binding
  events may be mediated by distinct surface
  interactions)

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Mucosal Immunology - Introduction

• Mucosal immunity protects internal epithelial
  surfaces.
• Components of the mucosal immune system include
  lymphoid elements associated with internal
  surfaces of the body (GI, respiratory,
  urogenital) and exocrine secretory glands linked
  to these organs, such as the salivary, lachrymal,
  pancreas, and mammary glands.

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Mucosa-associated lymphoid tissue (MALT)
Examples - Nasal-associated lymphoid tissue
(NALT). - tonsils, adenoids. - Gut-associated
lymphoid tissue (GALT). - Peyers patches. -
Bronchus-associated lymphoid tissue (BALT)
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Oral Tolerance
- Oral tolerance is the generation of systemic
immune unresponsiveness by feeding of antigen.
The antigen is usually soluble and without
adjuvant or proinflammatory activity. - Oral
tolerance is likely a mechanism for prevention of
harmful immune responses to harmless antigens
such as foods. - A number of mechanisms may
underlie oral tolerance, including clonal
deletion, clonal anergy, or active suppression by
T cells (cytotoxic, TH2, or TGF-? producing)
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ucosal Immunology- Lecture Outline -