Immunology

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
2. …