lymphoid organs

Examples of lymphoid organs in the following topics:

• Clonal Selection and Tolerance

  • Central tolerance is distinct from periphery tolerance in that it occurs while cells are still present in the primary lymphoid organs (thymus and bone-marrow), prior to export into the periphery.
  • Negative selection is the process that eliminates developing lymphocytes whose antigen receptors bind strongly to self antigens present in the lymphoid organs.

• Cells and Organs of the Immune System

  • The immune system includes primary lymphoid organs, secondary lymphatic tissues and various cells in the innate and adaptive immune systems.
  • The key primary lymphoid organs of the immune system include the thymus and bone marrow, as well as secondary lymphatic tissues including spleen, tonsils, lymph vessels, lymph nodes, adenoids, skin, and liver.
  • The red bone marrow is a key element of the lymphatic system, being one of the primary lymphoid organs that generate lymphocytes from immature hematopoietic progenitor cells.
  • Lymphoid tissue is found in many organs, particularly the lymph nodes.
  • Recognize the cells and organs of the immune system and their functions

• Development of the Dual Lymphocyte System

  • During this process, all lymphocytes originate from a common lymphoid progenitor before differentiating into their distinct lymphocyte types.
  • B cells mature into B lymphocytes in the bone marrow, while T cells migrate to, and mature in, a distinct organ called the thymus.
  • Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the spleen and lymph nodes) where they survey for invading pathogens and/or tumor cells.
  • All lymphocytes originate during this process from a common lymphoid progenitor before differentiating into their distinct lymphocyte types.

• Dendritic Cells

  • Dendritic cells are present in lymphoid organs, the epithelia of the skin, the gastrointestinal and respiratory tracts, and in most parenchymal organs.

• Classes of T Cells

  • Their name refers to the organ from which they're produced: the thymus.
  • These include naive T cells that recognize antigens and are activated in peripheral lymphoid organs.

• Cardiovascular and Lymphatic System Defenses

  • Lymphatic organs play an important part in the immune system, having a considerable overlap with the lymphoid system.
  • Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated with the digestive system such as the tonsils.
  • Lymphoid tissues contain lymphocytes, but they also contain other types of cells for support.
  • The first attach invading micro organisms directly while others produce antibodies that circulate in the blood and attack them.
  • When micro-organisms invade the body, or the body encounters antigens (such as pollen), antigens are transported to the lymph.

• The Complement System

  • The complement system helps antibodies and phagocytic cells clear pathogens from an organism.
  • Specific activation of the complement via innate recognition proteins or secreted antibody releases cleavage products that interact with a wide range of cell surface receptors found on myeloid, lymphoid, and stromal cells.
  • Further study in animals bearing natural complement deficiencies implicated the classical pathway as a crucial mechanism for efficient antigen trapping and retention in lymphoid tissues (e.g., splenic follicles), suggesting that a major function of the complement system was to localize foreign antigens into immune sites important for lymphocytes responses.

• Cell-Mediated Autoimmune Reactions

  • This requirement of a T cell can be bypassed in rare instances, such as infection by organisms producing super-antigens, which are capable of initiating polyclonal activation of B cells, or even of T cells, by directly binding to the β-subunit of T cell receptors in a non-specific fashion.
  • DQ is one of several antigens involved in rejection of organ transplants.
  • As a variable cell surface receptor on immune cells, these D antigens, originally HL-A4 antigens, are involved in graft versus host disease when lymphoid tissues are transplanted between people.

• Antibody Genes and Diversity

  • V(D)J recombination takes place in the primary lymphoid tissue (bone marrow for B cells, and thymus for T cells) and nearly randomly combines variable, diverse, and joining gene segments.
  • SHM diversifies B cell receptors used to recognize antigens and allows the immune system to adapt its response to new threats during the lifetime of an organism.
  • Antibody genes also re-organize in a process called class switching, which changes the base of the heavy chain to another.

• Making Memory B Cells

  • All these events occur in the highly "eventful" germinal centers of lymphoid follicles, within the lymph nodes.