6.4 Host Defense Mechanisms in the Respiratory Tract
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Describe the organization of lymphoid tissues associated with the respiratory track
- BALT (Bronchus Associated Lymphoid Tissue) is part of a larger system of lymphoid tissue associated w/ mucosal membranes (MALT)
- Both T and B cells are located here and it's main response is IgA antibody
Describe the mechanism responsible for preferential recirculation of lymphocytes to mucosal sites
What are the innate host defense mechanisms that are involved in protecting the respiratory track from pathogens?
- Anatomical barriers
- Cilia and mucus
- Cells and molecules
What are the adaptive host defense mechanisms that are involved in protecting the respiratory track from pathogens?
- B cells - secretory IgA
- T cells
What is granuloma?
- Organized collection of macrophages
- Macrophages fuse together to form multi-nuclear Langerhans giant cells
- May contain lymphocytes (T and B), neutrophils, dendritic cells, fibroblasts, and collagen
Describe the immunologic mechanisms involved in granuloma formation
- Analogous to a Type IV Hypersensitivity reaction
- Alveolar macrophages phagocytize pathogen (M. tuberculosis)
- Macrophages secrete cytokines and chemokines
- IL-1, IL-6, TNF-a
- IL-10, IL-12, IL-18
- Antigen processed and presented to CD4+ and CD8+ T lymphocytes
- T lymphocytes (primarily CD4+) are activated and secrete cytokines (IFN-y, IL-2)
- TH1 cells preferentially stimulated
- Inflammation initiated resulting in formation of granuloma and walling off of pathogen
What is serum IgA?
- Monomeric IgA
- Types: IgA1 and IgA2
How is secretory IgA produced?
- Antigen is transported across the epithelium by M cells to the lamina propria where they are processed by resident macrophages (APC)
- The processed antigen is presented by class II HLA bearing APC to CD4 T cells
- The T cells activate B cells to produce IgA dimers which are secreted and bind to a receptor, the polymeric immunoglobulin receptor, on the epithelium cell
- The complex of receptor and IgA crosses the epithelium and is exocytosed into the gut lumen
- A portion of the receptor remains w/ the IgA dimer forming the secretory component (SC)
- The complex of IgA dimer, J chain, and SC comprises secretory IgA
Identify J chain and secretory component
J chain -
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