Lymphoid organs

Synonym: lymphatic tissues
German: Lymphatische Organe

1 Definition

Lymphoid organs are certain organs respectively parts of tissues, in which lymphocytes can differentiate and proliferate. They are part of the lymphatic system.

2 Classification

The lymphoid organs can be classified into primary and secondary lymphoid organs.

2.1 Primary lymphoid organs

The primary lymphoid organs consist of specialized tissue, in which generation and maturation of B- and T-Lymphocytes takes place. The group of primary lymphoid organs contains the following:

• Thymus
• Bone marrow

During the fetal period the liver is also classified as a primary lymphoid organ. The lymphocytes which originated in these primary lymphoid organs immigrate into and respectively colonize the secondary lymphoid organs.

2.2 Secondary lymphoid organs

Processes of antigen contact and clonal proliferation of lymphocytes are taking place in secondary lymphoid organs. In this process effector cells as well as regulator cells are generated. This differentiation is located in the zone of proliferation of the secondary lymphoid organs. They contain the following:

• Mucosal lymphoid follicles (MALT)
  • Peyer's plaques
  • Vermiform appendix
  • Tonsils
• Lymph nodes
• Spleen, white pulp of the spleen