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Lymphoid organs

4 Pages

Course Code
BIOL 2005
Elizabeth Nisbet

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LYMPHOID ORGANS highly localized microenvironments are structural basis of immune response lymphocyte specificity is quite rare, as is their dispersement throughout the body soln: highly orchestrated movements of antigen 3 functional environments – 1) PRIMARY lymphoid organs – mature but naïve lymphocyte production 2) SECONDARY – mechanism of co-localizing antigens and lymphocytes 3) TERTIARY – sites of infection must be able to survey for it and also regulate the influx of effector cells PRIMARY LYMPHOID TISSUE – bone marrow and thymus antigen recognition development positive/negative selection signaling apparatus in response to antigenic stimulation capacity to home to proper microenvironment BONE MARROW – for B Cells contains no lymphatic channels but is vascularized hematopoetic stem cells are nestled next to osteoblasts and receive survival signals from them antigen independent maturation of B-cells very inefficient process (frameshift recombinations) pro-thymocyte also is made from hematopoetic stem cell stromal cells: support development/maturation of lymphocytes in marrow secrete cytokines (IL-7) C-KIT and stem cell factor interact on B-cell surface for lymphopoesis cell-cell contact w/ stromal cells also directs lymphopoesis THYMUS – many epithelial-derived cells CORTEX: CAPSULE = lining; invaginates to form lobes lined w/ early T-cell progenitors Cortical Epithelial Cells – dendridic cells, stimulate T-cell maturation Macrophages – clearance of unproductive rearrangements Interdigitating Cells – boundary between cortex and medulla also called “thymic dendridic cells” bone-marrow derived MHCI/MHCII presentation Localization of T-Cell Development- progenitors enter via capsule first replicate then undergo gene rearrangments CD4+/CD8+ developed that also have productive a/b TCR recombination Cortical Thymocytes then associate with epithelial cells  positive sel. CD4+ OR CD8+ singly positive cells can proceed based on MHCI vs MHCII affinity Interdigitating Cells – drive negative selection (self-recognition) **still unclear as to whether positive or negative selection occurs first** Stains: cytokeratin – stains for epithelial (dendridic) cells in thymus CD8 – stains for any cell with CD8+ (double-positives also stain) SECONDARY LYMPHOID TISSUES – lymph nodes (true and musocal), spleen - mechanisms for APC or antigen to access necessary microenvironment from site of infection - specialized vascularization (lymphatics and high endothelial venules) to recruit lymphocytes and send them back out (effect lymphatics) - distinct regions for B (follicles) and T cell priming (between follicles) FOLLICLES – primary follicles – B cells have not yet encountered antigen secondary follicles – rapid growth
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