The spleen, located in the left upper abdomen, has two major compartments: the red pulp, which functions as a filter for particulate antigens and for the formed elements of the blood, and the white pulp, which is virtually identical in its compartments to the lymphoid tissue of the lymph node. Follicles and germinal centers are found in the Malpighian corpuscles, while T cells and IDC are found in the adjacent periarteriolar lymphoid sheath. Plasma cells accumulate in the red pulp. The white pulp has two components: the eccentric follicles (Malpighian corpuscles) seen in Figure 1, and the periarteriolar lymphoid sheath seen here. The follicles are identical to lymph node follicles (B cell zones), while the periarteriolar sheath is identical to lymph node paracortex (T cell zone).