Compartmentalization of Human Thymic Medulla: Facts and Hypotheses

The thymus function was discovered in the middle of the last century. The role of the thymus in the adaptive immune system facilitated its histological and experimental studies. Before the role of the thymus was discovered, the thymus was called as a gland on the basis of lobulation; even some histological textbook listed it up among the endocrine glands. In addition to the cortex and medulla, the immunohistochemical studies revealed a further compartmentalization in the thymic medulla, which is related to the epithelium-free areas (EFA) and keratin-positive network (KPN). The two medullary compartments have different cellularity that determines their role. This chapter would concentrate on the medullary compartmentalization and their cellularity. Furthermore, this chapter discusses the relationship of thymic septae with the perivascular space, the vascular embedding and thymic dendritic cells.