Adaptive response; where and when? Flashcards
What are the primary lymphoid organs?
The bone marrow and thymus
What are the secondary lymphoid organs?
Lymph nodes, MALT (mucosa-associated lymphoid tissues) and spleen.
What are immune cells derived from?
All cells, except for FDCs are derived from hematopoietic stem cells in the bone marrow.
Blood infections primarily activate which secondary lymphoid organ?
The spleen
Tissue infections primarily activate which secondary lymphoid organs?
Lymph nodes.
Mucosal surface infections primarily activate which secondary lymphoid organs?
The mucosal associated lymphoid tissues which line respiratory, gastrointestinal and genitourinary tracts.
What process generates the specialised cells of the immune system?
Haematopoisesis
Desribe Haemotpoietic stem cells.
They are self-renewing in the bone marrow and are multipotent. There are two pathways; the myeloid and lymphoid. Multipotency is lost when develop into common myeloid/lymphoid progenitor cells.
Which cells arise from the myeloid pathway?
erythrocytes, thromobytes, myeloid dendritic cells, monocytes, neutrophils, eosinophils, basophils, mast cells.
Which cells arise from the lymphoid pathway?
B and T precursor cells, NK cells, lymphoid dendritic cells. T cell precursors must enter thymus for further specialisation into t cells through recombination of their TCR genes.
What occurs once lymphocytes are produced?
Recirculation via blood circulation and lymphatic system.
What is the Thoracic duct?
The main connection between the blood and lymphatic systems.
How do lymphocytes enter lymph nodes and MALT?
They enter these structures from the circulation, leaving the blood vessels via specialised ares of vascular endothelium termed the high endothelial venules (HEV) directly into the lymph node. They can enter inflammed tissued via diapedesis. Lymph nodes have afferent and efferent systems
What does recirculation enable?
Lymphocyte recirculation allows antigen reactive cells to home to the places where they are required with a targeted migration of lymphocytes into the sites where infection may be present. This traffic is mediated through homing molecules on the lymphocyte surface with recognises vascular addressins on the blood vessel endothelium.
Describe the structure of the lymph node.
Has an outside collagenous capsule and is connected to the blood circulation. Cortex = outer area and medulla = inner area. Between the cortex and medulla is the paracortex. Main cells in lymph nodes are lymphocytes which are organised into lymphoid follicles.
What is the relationship between dendritic cells and lymph nodes?
Dendritic cells recognise PAMPs/DAMPs via PRRs and migrate carrying antigen to the lymph nodes via afferent lymphatics. IDCis now in the lymph node where its long processes interact with T lymphocytes, which has costimulatory molecules (B7). IDCs present antigen to T cell in the paracortex.
What do FDCs do?
Present antigens and immune complexes to B cells in the germinal centres of lymph nodes.
What are germinal centres?
These are organised strucutres in the secondary lymphoid tissues where all the cells required to initiate an adaptive immune response, such as dendritic cells, helper T cells and B cells, can interact optimally with each other. These are the sites of T and B memory cell generation, antibody class switching, somatic hypermutation (affinity maturation) of B cells and the generation of the precursors of antibody-secreting plasma cells.
Describe the anatomy of germinal centres.
Mantle zone, centroblast dark zone, centrocyte in basal light zone, centrocyte in apical light zone. Naive B cell net migration is unidirectional through mantle zone to centrocyte apical light zone
Describe the structure of the spleen
There is red and white pulp, with RBS and leukocytes respectively. The periarteriolar lymphoid sheath is a T cell area of white pulp. Within lymphoid sheath if there is an antigen, maturation processes common to lymph nodes.
Describe MALT immunity.
Where most infections enter the body, mucous secretions prevent adhesion of pathogens so colonisation cannot occur. Dimeric secretory IgA is transported into the gut by poly-Ig receptors at mucosal surfaces. Dimeric secretory IgA are held together by J chains; a polypeptide. The poly-g (Ig receptor recognises polymerised Igs, also recognises pentameric IgM as it also has a J chain.) Poly-Ig receptor binds to dimeric IgA at basal surface and the complex is then endocytosed by the glandular epithelial cell where it is transported in a vesicle to the apical mucosal surface and is exocytosed. Poly-Ig receptor is then cleaved at apical surface. secretory piece of poly-Ig receptor protects the dimeric IgA and prevents adhesion. IgA is the most important for MALT immunity.
What is the most common antibody in the cirulation?
IgG
What is the second most common class of antibody?
IgA
Where is secretory IgA produced?
At mucosal surfaces produced by plasma cells underlying the mucosal surface. Secretory IgA is dimeric IgA.
