Periarteriolar lymphoid sheaths (or periarterial lymphatic sheaths, or PALS) are a portion of the

white pulp White pulp is a histological designation for regions of the spleen (named because it appears whiter than the surrounding red pulp on gross section), that encompasses approximately 25% of splenic tissue. White pulp consists entirely of lymphoid ti ...

of the

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

. They are populated largely by

T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

s and surround central arteries within the spleen; the PALS T-cells are presented with blood borne antigens via

myeloid dendritic cells Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. The ...

. In contrast, the

lymphoid The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system, and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphatic or lymphoid o ...

portions of the white pulp are dominated by B cells.

External links

* *
Diagram at okstate.edu

{{lymphatic-stub Lymphatic organ anatomy