Mucosal Immunity and Immunology Quiz

Mucosal Immunity

• The adult gut processes over 1 ton of nutrients per year, with a large surface area specialized for absorption, spanning around 400m².

Systemic vs. Mucosal Immunity

• Mucosal tissues encounter undefined antigens continuously, whereas systemic environments encounter them rarely.
• Mucosal immunity is essential for protection against pathogens, preventing hypersensitivity to foods and commensal organisms, and for vaccine development.

Mucosal Tissues and Cells

• Mucosal associated lymphoid tissue (MALT) includes inductive and effector sites, such as NALT (Nasal), GALT (gut), and others.
• Peyer's patches contain 50% B cells, 30% T cells, and 8% macrophages, with few plasma cells.
• Isolated lymphoid follicles (ILFs) are induced by commensal gut microorganisms and contain mainly B cells, some T cells, and dendritic cells.

Peyer's Patches and ILFs

• Peyer's patches are inductive sites of GALT, connecting to the lymphatic system only by efferent lymph vessels.
• B lymphocytes from Peyer's patches give rise to IgA-producing plasma cells that home to all mucosal sites.

M Cells

• M cells are specialized epithelial cells that take up and transport particulate antigens, located above Peyer's patches and ILFs.
• M cells are targets for particles, viruses, parasites, and bacteria, including cholera toxin, poliovirus, HIV, and more.

Cells of Mucosal Immune System

• Conventional cells include dendritic cells, macrophages, neutrophils, mast cells, eosinophils, and basophils.
• Specific cells include epithelial cells, M cells, intraepithelial lymphocytes (IELs), and lamina propria T cells.

Lamina Propria T Cells

• Lamina propria T cells are mainly CD4+, produce cytokines, and express α4β7 integrin.
• T cell subsets include Tregs, Th1, Th2, and Th17, each with distinct functions and cytokine production.

Intraepithelial Lymphocytes (IELs)

• IELs are mainly CD8+, express αEβ7 integrin, and are unresponsive to TCR stimulation.
• IELs can be derived extrathymically and recognize MadCAM and CCL25, homing to mucosal tissue.

Lymphocyte Homing

• Homing involves chemokines, rolling adhesion, and tight adhesion, facilitated by α4β7 integrin and MAdCAM-1.
• Further migration occurs through chemokine recognition, such as CCL25 and CCL20, and adhesion through E-cadherin.

B Cell Function: Secretory IgA

• Secretory IgA is produced by mucosal B cells and is essential for mucosal immunity.
• IgA production is influenced by TGFβ and IL-5 and has different functions and activities compared to IgG.

Oral Tolerance

• Oral tolerance requires a functional immune system and symbiosis with commensal organisms.
• Features of oral tolerance include antigen specificity, partiality, and a quantitative reduction in antibody levels, which wane with time.