Final: Lecture 18 Flashcards
0
Q
Acquired Immunity
A
- Develops in response to antigens
- More powerful than innate immunity
- Takes longer to develop
- Displays specificity and memory
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Innate Immunity
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- Lacks immune specificty and memory, what you’re born with
- Response = Inflammation
- Neutrophils are the first responders
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Lymphoid tissue
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•Appears in body as a gradient from diffuse lymphoid tissue to aggregated lymphoid tissue to lymphoid organs
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Passive immunity
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•Temporary immunity due to dontated antibodies (i.e. transplacental passing of maternal antibodies to fetus)
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Active immunity
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•Long-lasting/permanent immunity due to self exposure to antigen resulting in memory T cells and B cells specific for antigen
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Lymphoid organs
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- Primary: thymus and bone marrow
* Secondary: lymph nodes, spleen, tonsils
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__________ originate in primary lymphoid organs and then take up residence in secondary lymphoid organs.
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•Lymphocytes
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Lyphopoiesis
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- All immune system cells originate in bone marrow
- Immature T cells travel to thymus
- B-cells travel to specific regions in lymphoid tissue
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Antibodies (Immunoglobulins)
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- 5 classes: IgA, D, G, M, and E
- Light and heavy chains
- Highly variable regions: fab fragment, recognizes antigen
- Less variable regions: Fc fragment, binds antibody to cells
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Q
IgA
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•Found in saliva, milk, GU and respiratory tracts
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IgD
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•Found on surface of B cells traveling to lymphoid organs
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IgG
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- Major Ig in blood
* Responsible for most antibody activity, only one capable of crossing the placenta
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IgE
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•Associated with allergic responses
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IgM
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•First antibody class expressed by developing B cells
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B cells
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- Maturation involves the appearance of certain cell surface receptors
- IgM and IgD, MHC class II proteins, complement receptors, Ig Fc receptors
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Major Histocompatibility Complex
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- Function: Main function of MHC gene products is the presentation of antigenic peptides to T cells
- MHC 1: Expressed on the surface of all cells except trophoblasts and RBC
- MHC II: Expressed on the surface of B cells and antigen-presenting cells
16
Q
CD8+ T cells recognize _____ _____ of foreign proteins bound to MHC class I on the surface of cells.
A
- Peptide fragments
- CD8 member of the Ig superfamily
- Both the CD8 and T cell antigen receptor are required for the binding of MHC class I protein fragments
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CD4+ T cells also recognize ____ ______ of foreign proteins bound to MHC class proteins on surface of ___.
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- Peptide fragments
* APCs
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T cells
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- Pre-T cells develop in bone marrow
- Travel to thymus and complete maturation
- CD4+ T cells: recognize antigens bound to MHC class II molecules
- Helper cells: assist CD8+ cell differentiation, assist B cell differentiation
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CD8+ T cells
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- Cytolytic T cells (kills cells)
- Bind to an antigen presenting cell, undergo mitosis
- Release perforins and Fas ligand
- Recognize antigens bound to MHC class I molecules
- Mediators of cellular immunity
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Q
CD16+ T cells
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- Natural killer (NK) T cells
- Activated (by tumor cell antigens) T-helper cells release cytokines: Interleukin-2, Interferon-gamma, Macrophage activating factor (MAF), chemotactic factor, tumor necrosis factor
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Interleukin-2
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•Stimulates proliferation of NK cells
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Interferon-y
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•Activates NK cells
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MAF
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•Activates macrophages
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Tumor necrosis factor (TNF-ß)
•Kills tumor cells directly
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T cells recognize _____ _____ only when they are presented bound to MHC.
•peptide antigens
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MHC restriction
* Cytolytic T cells recognize an antigen presented by class I MHC molecules
* Helper T cells recognize an antigen is association with class II MHC
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Foreign proteins are broken down into fragments, some of which have antigenic properties called ______.
•Epitopes
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Activated T cells undergo mitosis, some daughter cells become ______ cells, while others secrete _______.
* Memory cells
| * Interleukins
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B cells undergo mitosis, some daughter cells become ______ cells, while others become _______ cells.
* Plasma, secrete appropriate antibodies
| * Memory
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What is the role of Perforin?
•Pokes holes in cell membranes to kill the infected target cell
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The cytolytic T cells protects itself from perforin with _______.
•Protectin, binds to perforin
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___ _____, released by the cytolytic T cell and bound to the ___ receptor, together with granzye destroy by apoptosis the target cell.
* Fas ligand
| * Fas
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Complement system
* Is an array of about 20 serum proteins which are synthesized in the liver and found in the blood
* Facilitates inflammatory response
* Either pathway involves coating the pathogen with complement initiating cascade
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Classic pathway
•Cascade is activated by antibody binding to a pathogen
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Alternate pathway
•Cascade is directly activated by the pathogen
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Activation Sequence
* C1(the first complement factor in the cascade) is made up of three subcomponents.
* Immunoglobulins bind to surface of pathogen
* C1q binds to Fc region of Ig-->activates C1r-->activates C1s--->initiates complement cascade
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Activation Sequence after C1s
* C1s--> C4-->C4a + C4b (binds to surface of pathogen)
* C1s-->C2-->C2a + C2b
* C2b binds to C4b-->C4b - 2b complex (=C3 convertase)
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Activation Sequence after formation of C3 convertase
* C3 convertase-->C3-->C3a + C3b (most important opsonin)
| * Multiple C3b bind to C3 convertase-->C4b - C2b - C3b complex (= C5 convertase) ** really attracts macrophages
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Activation Sequence after formation of C5 convertase
* C5 binds to C3b-->C5a + C5b
| * When C6, C7, and C8 are added to the complex, they form pores in the membrane of the pathogen. (KILL IT)
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The complement cascade results in the following:
* activation of the membrane attack complex (MAC) on the pathogen leading to perforations and lysis
* Production of opsonins, which are coatings that make the antigen more palatable to phagocytes
* Release of chemotactic agents (chemokines) which attract phagocytes (chemotaxis) to the areas of infection or inflammation
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Parenchyma
* Consists of the cells that typically pack areas of the lymphoid organ
* Mostly lymphocytes
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Stroma
•Consists mostly of reticular fibers and cells, including undifferentiated cells and fixed and free macrophages
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Lymph follicles (nodules)
* Gross structure: not encapsulated, cortex of dense, small lymphocytes, germinal center (only present if immune response is going on) of proliferative lymphocytes
* Transient
* Vascular supply: arteriole and venule supply the cortex, another supplies the center, lymph capillaries are not present
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Lymph node Hilus
* Entry and exit point for vessels
* Efferent lymphatic vessels as well as arteries and veins enter, carrying away from node
* Afferent enter the convex side of the node
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Lymph node Capsule
•Dense collagen fibers, some elastic fibers and smooth muscle fibers
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Lymph node Cortex
* Outer: contains lymph follicles (nodules)
* Follicles: contain B cells, follicular/migrating dendritic cells, secondary (mantle and germinal center), and primary (lack mantle and germinal center)
* Deep (inner): Contains Th cells, macrophages, high endothelial venuels (HEVs, port of entry for circulating differentiated lymphocytes to see lymph nodes)
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Lymph node Medulla
* Irregular arrangement of loose medullary sinuses (lined with macrophages) and dense medullary cords (consist of blood vessels, lymphoblasts and plasma cells)
* Site of lymphocyte reentry into lymph stream
* Thymic-dependent areas in subcortical and deeper medullary regions, have primary T cells
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Thymus Histology
* Capsule: blood vessels, no lymphatics
* Septa: delicate CT
* Most developed at puberty: 10-15 grams at birth, 30-40 at puberty
* Involutes during adolescence, no lymph follicles, afferent lymph vessels, or lymph sinuses
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Thymus Cortex
* Cortex (dark staining): small lymphocytes and immunoblasts
* thymocytes migrate from cortical areas to medually
* blood vessels surrounded by continuous epithelial barrier (allows to maintain lymphopoiesis while segregated from antigens)
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Thymus Medulla
* Light staining, specialized to allow entry channel into blood stream of differentiating lymphocytes
* Capillary beds are not sheathed by epithelial cells
* Hassall's corpuscles: whorls of highly keratinized medullary epithelial cells, produce cytokine thymic stomal lymphopoietin
* Stimulates thymic dendritic cells needed for the maturation of single positive T cells
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Differentiation of T cells**
* Double negative
* Double positive T cells move to outer cortex
* Single positive move to inner cortex: express TCR receptors and either CD4 or CD8 coreceptors
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Double negative T cells
* Lack cell surface molecules typical of mature T cells
* Enter cortex from blood vessels
* Proliferate in subcapsular area*
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Double positive T cells
* Move to outer cortex
* Confronted with epithelial cells with cell surface MHC classes I and II for clonal selection (if you aren't good enough, they will kill you!!!)
* Express both CD4 and CD* coreceptors and TCR receptors
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Spleen Morphology
* 5.6 x 4 inches, no lymph sinuses or afferent lymph vessels
* Covered by peritoneum except at hilus
* Blood vessels enter and leave hilus
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Spleen Functions
* Only lymphatic organ specialized to filter blood
* Stores and removes worn-out RBCs
* Recycles iron
* Converts hemoglobin to bilirubin
* blood formation in the fetus
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Spleen Immunologic functions
* Sreens foreign material in the blood
* Produces lymphocytes and plasma cells (produced in bone marrow, activated by spleen)
* Removal leads to overwhelming bacterial infections in infants, children, and young adults
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Spleen Histology
* Capsule: thin, dense fibrous CT with elastic fiber and some smooth muscle
* Trabeculae: extend inward from capsule, covered by mesothelium
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Spleen Parenchyma
* B cells located in the peripheral white pulp, often have germinal centers
* T cells found in the areas surrounding the central artery near the center of white pulp
* Reticular fibers are associated with fixed macrophages and support splenic pulp
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Spleen White Pulp
* Elongated, branched strands always associated with arteries
* Zones of diffuse lymphoid tissue and germinal centers (contain B cells)
* Lymph follicles, chief site of lymphocyte production
* T-cell areas surround follicles and periarteriolar sheaths (PALS)
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Spleen Red Pulp
* Surrounds white, contains large number of RBCs
| * Cords of lymphoblasts and plasma cells = Billroth cords
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Spleen Vascularization
* Arteries: splenic enters at hilus, trabecular arteries branch off
* Central arteries: adventitia (CT) loosens and becomes mesh-like reticulum infiltrated with lymphocytes
* After capillaries form, supplying white pulp, central arteries lose their white pulp investment and enter red pulp to form penicillus
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Penicillus
* composed of pulp arteriole, sheathed arteriole, and terminal capillary
* Terminal cap. drains into intercellular spaces (open system) or venous sinuses lined with reticuloendothelial cells (closed system)
