Gastrointestinal Defense Mechanisms Acidity in the stomach ...

Gastrointestinal Defense Mechanisms

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


• 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


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


• 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


• “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”



• 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


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


• 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

Mucosal Immunology

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



• 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


• 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.


• 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


• 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

GUT ASSOCIATED LYMPHOID TISSUE(GALT)

• One of the major subdivisions of the immune system

• 25% of intestinal mucosa is lymphoid tissue

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

Mucosal uptake of bacteria

• M cells are found in the epithelium overlaying Peyer’s patches

Characteristic features of MALT

M cells facilitate antigen uptake.

M cells

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

M cells


• Serve as a channel for entry of molecules into the underlying mucosal follicular region

M cells


• 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)

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.

Mucosa-associated lymphoid tissue (MALT)

Examples:- Nasal-associated lymphoid tissue (NALT).

- tonsils, adenoids.- Gut-associated lymphoid tissue (GALT).

- Peyer’s patches.- Bronchus-associated lymphoid tissue (BALT)

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)

ucosal Immunology- Lecture Outline -

Gastrointestinal Defense Mechanisms Acidity in the stomach ...

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