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Principles of Immunology�Organs of the Immune System 1/31/06�

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“There are two ways to slide easily through life. Believe everything or doubt everything. Both ways save us from thinking.”

A Korzybski

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Word List

  • Antigenic commitment
  • Clonal proliferation
  • GALT
  • Lymph
  • Lymphocyte activation
  • MALT
  • Peyer’s patches
  • Primary lymphoid organs
  • Secondary lymphoid organs
  • Self antigens

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Lymphoid System

  • Primary lymphoid organs
    • Bone marrow
    • Thymus

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  • Secondary lymphoid organs
    • Organized
      • Lymph nodes
      • Spleen
    • Less organized

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Lymphatic System

  • Network of vessels
    • Collects fluid from tissues
    • Major cell is lymphocyte
    • Unidirectional
    • Often first place where antigens are detected

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Thymus

  • Structure
    • Gross
      • Bi-lobed
      • Lies above heart
    • Microscopic
      • Capsular
      • Lobules with outer cortex and inner medulla

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Thymus

  • Function
    • Takes in immature T cells and puts out mature (immunocompetent) T cells
    • Increased diversity of T cells
    • T cell selection

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Thymus

  • T cell selection
    • Based on MHC/Ag complex recognition
      • Recognize MHC/Non self AG complexes
      • Recognize MHC/Self Ag complexes
      • Do not recognize MHC/Ag complexes

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  • Athymic condition
    • Natural
    • Other

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Bone marrow

  • Structure
    • Microscopic
      • Less well defined than thymus
      • Role of stromal cells

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  • Function
    • Hematopoiesis
    • B cell maturation
    • B cell selection
    • Puts out mature, naive B cells

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Lymph Nodes

  • Structure
    • Gross
      • Bean-shaped structures
      • Drains major segments of lymphatic system

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Lymph Nodes

  • Structure
    • Microscopic
      • Major cell types
        • Lymphocytes
        • Macrophages
        • Dendritic cells
      • Cortex/paracortex/medulla
      • Follicles
        • Primary
        • Secondary

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Lymph Nodes

  • Function
    • 1st line of response to antigens
    • Secondary follicle (Germinal center) is site of B cell proliferation, mutation, differentiation
    • Specificity is high
    • >90% of B cells die through apoptosis
    • After Ag stimualtion lymphocyte numbers up by 50X in efferent lymphatic vessel
    • Lympadenopathy

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Spleen

  • Structure
    • Gross
      • Ovoid organ in upper left quadrant of abdomen
    • Microscopic
      • Compartmentalized
        • Red pulp
        • White pulp
      • Periarticualr lymphoid sheath
        • Site of Ag presentation
      • Major cell types
        • Lymphocytes
        • Macrophages
        • Dendritic cells
        • RBCs

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Spleen

  • Function
    • Filters out older RBCs
    • Responds to Ag in circulatory system
    • Produces activated B cells

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  • Splenectomy

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Tonsils

  • Follicular structure
  • Contains lymphocytes, macrophages, mast cells
  • Germinal centers appear in response to Ag
  • Protective role in URI

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Appendix

  • Associated with intestines
  • Responds to Ag
  • Role in GI immune response

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MALT

  • Lymphoid tissues below epithelium
  • Presence of B cells
  • Ag presented through unique cell (M cell)
  • Preferentially responds with IgA antibody

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