Mucosal Immunology

• Mucosal membranes cover the gastrointestinal tract, upper and lower respiratory tract, and urogenital tract.
• Mucosal barriers are relatively thin barriers but cover a large surface area. They have an associated microbiome. Pathogen entry across the mucosae is a common mechanism for causing disease.
• Immune cell locations in organised structures:

  • Mucosal associated lymphoid tissue (MALT)-some species specific differences
  • Peyer’s patches - small intestine
  • Lymphoid follicles- intestine
  • Tonsils
  • Draining lymph nodes connected with MALT via lymphatics
• Immune cell locations for scattered effector cells (healthy gut):

  • Epithelium
  • Lamina propria
• Gut associated lymphoid tissue (GALT) are lymphoid tissues in the gut covered by specialised epithelium which consists of enterocytes and microfold cells (M-cells) alongside lymphocytes and DCs.
• M-cells are part of a folded surface and have no mucous secretion or enzyme production. They sample microbiota and other particles by endocytosis or phagocytosis, allowing entry to lymphoid tissues.
• Dendritic cells aid in the uptake of antigens and present them to naïve T cells in Peyer’s patch. In turn they activate B-cells and then subsequently switch antibody classes to IgA. Primed lymphocytes leave via lymphatics to draining LN and through lymphatics to blood and then to mucosa. Lymphocytes return to mucosa as effector cells. Circulation may be required for differentiation.
• Intraepithelial lymphocytes have a role in recognition and killing of damaged epithelial cells as well as the repair of mucosa and suppression of inflammation.