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.

The spleen synthesizes antibodies in its white pulp and removes antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation.

Periarteriolar lymphoid sheaths (or periarterial lymphatic sheaths, or PALS) are a portion of the white pulp of the spleen.

The marginal zone is the region at the interface between the non-lymphoid red pulp and the lymphoid white-pulp of the spleen.

The spleen is made of red pulp and white pulp, separated by the marginal zone; 76-79% of a normal spleen is red pulp.

These macrophages are not unique to the spleen but instead make up an integral part of the lymphoid parts of all secondary lymphoid organs.

When these arteries then reach the white pulp, and become covered with periarteriolar lymphoid sheaths, the name changes again to central arteries (or central arterioles).

The T cell zone (periarteriolar sheath) and B cell follicles contain discrete macrophage populations; however, not much is known about these macrophage populations in terms of their origin and lifespan.

The T cell zone (periarteriolar sheath) and B cell follicles contain discrete macrophage populations; however, not much is known about these macrophage populations in terms of their origin and lifespan.

The T cell zone (periarteriolar sheath) and B cell follicles contain discrete macrophage populations; however, not much is known about these macrophage populations in terms of their origin and lifespan.

In the B cell follicles, the macrophages are important in clearing the apoptotic B cells that occur during the germinal centre reaction in the process of somatic hypermutation and isotype switching.

In the B cell follicles, the macrophages are important in clearing the apoptotic B cells that occur during the germinal centre reaction in the process of somatic hypermutation and isotype switching.

In the B cell follicles, the macrophages are important in clearing the apoptotic B cells that occur during the germinal centre reaction in the process of somatic hypermutation and isotype switching.

B cells that cannot form their appropriate receptors will die of apoptosis and are subsequently cleared by the macrophages in the germinal centre.

During intensive germinal centre reactions, this process is obvious due to the presence of the large macrophages in the germinal centre, known as tingible body macrophages.

(They're named this because their 'tingible bodies' represent condensed apoptotic nuclei.) In order for the apoptotic cells to be taken up by macrophages, it is important that phosphatidylserine is expressed on the outer surface of the apoptotic cells, which is recognized by multiple receptors.

It is possible that these macrophages are descendants of patrolling monocytes that entered the white pulp from the blood.

Due to them being positioned alongside T cells, it is suggested that these macrophages have a role in antigen presentation or the removal of dying lymphocytes.

Due to them being positioned alongside T cells, it is suggested that these macrophages have a role in antigen presentation or the removal of dying lymphocytes.