A novel aspect of the structure of the avian thymic medulla

Abstract

We provide evidence for the compartmentalization of the avian thymic medulla and identify the avian thymic dendritic cell. The thymic anlage develops from an epithelial cord of the branchial endoderm. Branches of the cord are separated by primary septae of neural crest origin. The dilation of the primary septae produces the keratin-negative area (KNA) of the thymic medulla and fills the gaps of the keratin-positive network (KPN). Morphometric analysis indicates that the KNA takes up about half of the volume of the thymic medulla, which has reticular connective tissue, like peripheral lymphoid organs. The KNA receives blood vessels and in addition to pericytes, the myoid cells of striated muscle structure occupy this area. The myoid cells are of branchial arch or prechordal plate origin providing indirect evidence for the neural crest origin of the KNA. The marginal epithelial cells of the KPN co-express keratin and vimentin intermediate filaments, which indicate their functional peculiarity. The basal lamina of the primary septum is discontinuous on the surface of the KPN providing histological evidence for the loss of the blood-thymus barrier in the medulla. In the center of the KNA, the dendritic cells lie in close association with blood vessels, whereas the B-cells accumulate along the KPN. The organization of the KPN and KNA increases the "surface" of the so-called cortico-medullary border, thereby contributing to the efficacy of central tolerance.

Acute Thymic Involution and Mechanisms for Recovery

“…Moreover, the entire thymic lobe resembled the medulla. Rapid regeneration of the thymus was observed after cessation of the DM treatment (Bódi et al 2015). However, the thymocytes from DP1 −/− mice were not sensitive to either systemic delivery of DM or in vitro DM treatment, which indicates the importance of this new DP-1 receptor pathway in bleomycin-induced ATI (van den Brule et al 2014).…”

“…The thymus is a unique lobulated lymphoid tissue that develops as a gland (Bódi et al 2015). It is considered a primary immune organ in jawed vertebrates, in which it plays important roles in the selection, proliferation, development and differentiation of T cells and provides protection against infections by various pathogens (Bajoghli and Guo 2011;Gameiro et al 2010;Liu et al 2014).…”

Avian coronavirus infection induces mannose-binding lectin production in dendritic cell precursors of chicken lymphoid organs

“…Contrary to the findings in the spleen, the CD83 shows separate 'patchlike' staining in the caecal tonsils (CT), which is similar to the staining pattern of CD83 in thymic dendritic cells of chickens (Bódi et al, 2015). In the CT MBL is expressed in both the control (Fig.…”

Compartmentalization of Human Thymic Medulla: Facts and Hypotheses

“…At the corticomedullary junction, PS merges to the PVS of the medulla [9,10]. A continuous basal lamina covers the thymic parenchyma toward the capsule and PS, and it becomes discontinuous at the end of the PS (Figure 1) [2,7] where it turns to be the PVS or KNA/ EFA. In the thymic medulla, the lack of blood-thymus barrier [16] may be explained by the discontinuity of the basal lamina on the border of the KNA/EFA [2].…”

“…The relatively simple structure of the thymus did not help to "decode" the enigmatic thymic function until the middle of the last century. The three morphological landmarks may be supplemented by the keratin-negative area (KNA) [1,2] or "epithelium-free area" (EFA) [3][4][5][6]. EFA can be found in both the cortex and medulla [6][7][8].…”