Updated: 6/8/2020

Primary Lymphoid Tissue

0%
Topic
Review Topic
0
0
N/A
N/A
Questions
2
0
0
0%
0%
Videos / Pods
1
Topic
Introduction
  • There are two primary lymphoid organs in humans including the
    • bone marrow
      • the site of development for B-cells
    • thymus
      • the site of development for T-cells
  • They serve as the site of adaptive immune cell maturation steps such as
    • replication of an
      • immature progenitor cell population
    • recombination of VDJ regions to
      • generate adaptive immune cell receptors
    • positive selection to remove
      • cells with defective surface receptors
    • negative selection to remove
      • cells that are reactive against self-antigens
  • Abnormalities in primary lymphoid tissue can result in
    • immunocompromise due to
      • failure of adaptive immune cell development
    • autoimmunity due to
      • failure of central tolerance mechanisms (negative selection)
Bone Marrow
  • Bone marrow is the site of pluripotent hematopoietic stem cells that can
    • differentiate into many different lineages of which the two relevant to immunity are
      • the lymphoid lineage, which
        • is stimulated by the cytokine IL-7
        • includes members of both the adaptive and innate immune response
          • B-lymphocytes (adaptive)
          • T-lymphocytes (adaptive)
          • NK cells (innate)
      • the myeloid lineage which
        • is stimulated by GM-CSF and IL-3
        • includes members of the innate immune response
          • monocyte/macrophage
          • eosinophils
          • mast cells
          • basophils
          • platelets
          • erythrocytes
          • dendritic cells
  • Bone marrow also serves as the site of B-cell maturation where
    • the B-cell receptor is recombined
    • immature B-cells undergo both positive and negative selection
Thymus
  • The thymus is a primary lymphoid organ that is This photomicrograph shows a hassall corpuscle, which is a characteristic feature of the inner medulla of the thymus and is composed of epithelial reticular cells.
    • located in the anterosuperior mediastinum
    • derived from the third pharyngeal pouch
    • bilobed in structure with a dense cortex and a pale medulla
    • the site of Hassall corpusles containing epithelial reticular cells
  • The thymus serves as the site of T-cell maturation where
    • the T-cell receptor is recombined
    • immature T-cells undergo both positive and negative selection
  • The thymus is composed of several regions including
    • an outer cortex region with
      • immature T-cells
      • a network of epithelial cells, dendritic cells, and macrophages
    • a corticomedullary region that serves as the site for
      • positive selection of T-cell receptor development
      • negative selection against autoimmune T-cells
    • an inner medullary region containing
      • mature T-cells
      • epithelial reticular cells
      • Hassall's corpuscles
Abnormalities
  • Abnormal development of primary lymphoid organs can lead to
    • immunodeficiency syndromes such as 
      • severe combined immunodeficiency (SCID)
      • thymic aplasia (DiGeorge syndrome) which 
        • is caused by 22q11 deletion leading to
          • failure to develop 3rd and 4th pharyngeal pouches
          • ↓ PTH due to parathyroid aplasia causing 
            • tetany due to hypocalcemia
          • T cell deficiency due to thymic aplasia leading to
            • recurrent viral/fungal infections
            • absent thymic shadow on CXR
          • congenital heart and great vessel defects
    • autoimmunity syndromes such as
      • myasthenia gravis associated with
        • development of a thymoma
      • generalized autoimmunity due to
        • failure of central tolerance

References

Please rate topic.

Average 4.6 of 9 Ratings

Questions (2)
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
VIDEOS & PODCASTS (1)
EXPERT COMMENTS (15)
Private Note