Immunology

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Preventing infection at mucosal tissues

  • mucosal surfaces are found trougout the body
  • massive surface area-400m2
  • fuctions: gas exachange, food absorbtion, senses
  • thin, permeable barriers
  • very vunerable to infection

MALT is dedicated to mucosal protection

  • Mucosal - Associated Lymphoid Tissue  
  • surrounds and protectes the mucosa 
  • similar anatomy to secondary lymphoid tissues
  • local initiation of adaptive immune responses - close to site of infection

mucosa is full of effector cells

  • healthy intestinal epithelium and lamina propria are populated with effector leukocytes
  • pyers patches protect small intestines
  • organized lymphoid tissue and single lymphoid follicules are present in gut wall
  • M cells sample antigens
  • -specialised to transport microorganisms to gut associated lymphoid tissue

Mcells select certain antigens

  1. Mcells take up antigen by endocytosis and phagocytosis
  2. antigen is transported across the M cells in vesicles and released at the basal surface
  3. antigen is bound by dendritic cells, which activate T-cells

DC can capture antigens too

  • dentritic cells can extend processes across the epithelial layer to capture antigen from the lumen of the gut

lymphocytes activated in MALT become commited to the mucosa

  • naive lymphocytes activated in a peyers patch give rise to effector cells that travel in the lymph and blood to gain access to the lamina prpria of the mucosal tissue

A chronic immune response

  • healthy mucosa maintains an adaptive immune response
  • M cells and DC constantly sample the gut contents
  • B and T cells are continuously stimulated
  • But no imflamtion - no T:R on macrophages
  • microorganisms are kept in the gut lumen, not in the tissues- commensal and pathogens
  • chronic stimulation- lymphocytes on standby for breach of defenses

mucosal immune sytem 

anatomical features

  • intimate interactions between mucosal epithelia and lymphoid tissues
  • discrete compartments of diffuse lymphoid tissue and more organized structures - peyers patches, isolated lymphoid follicles, tonsils
  • specialised antigen-uptake mechanisms provided by m cells in peyers patches, adenoids and tonsils

effector mechanisms

  • activated effector cells predominate even in the absense of infectio
  • plasma cells are in the tissues where antibodies are needed

immunoregulatory environment

  • dominant and active downregulation of inflammatory immune responses to food and other innocuous envirnmental antigens
  • inhibitory macrophages and tolerence-inducing dendritic cells

memory and secondary immune responses

  • 3 outcomes of succesful response
  1. clear infection

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