peripheral lymphoid organs

The peripheral lymphoid organs are the sites of lymphocyte activation by antigen.

Mature lymphocytes recirculate between the blood and the peripheral lymphoid organs until they encounter their specific antigen.

Histologic analysis indicates that peripheral lymphoid organs, particularly lymph nodes, lack the proper number of cells.

Secondary or peripheral lymphoid organs maintain mature naive lymphocytes and initiate an adaptive immune response.

Additionally, it acts as an adhesion molecule for leukocytes on peripheral lymphoid organs and inflammation sites.

In an adult animal, the peripheral lymphoid organs contain a mixture of B and T cells in at least three stages of differentiation:

Plasmacytoid dendritic cells (pDCs) are innate immune cells that circulate in the blood and are found in peripheral lymphoid organs.

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.

Tolerance can also be differentiated into 'Central' and 'Peripheral' tolerance, on whether or not the above-stated checking mechanisms operate in the central lymphoid organs (Thymus and Bone Marrow) or the peripheral lymphoid organs (lymph node, spleen, etc., where self-reactive B-cells may be destroyed).