Tissue Interaction in the Development of Thymus Lymphocytes

Abstract

Thymic rudiments from chick and mouse embryos have been cultured in diffusion chambers on the chick chorioallantois. In this situation their supply of blood-borne stem cells is cut off. Although rudiments from older embryos become fully lymphoid under these circumstances, primordia from early embryos fail to develop any lymphoid cells. Early chick rudiments will however develop completely if they are grafted directly to the chorioallantois where they receive a vascular supply. It is concluded that stem cells first enter the chick thymic anlage at between 6 and 7 days' incubation and the mouse thymic rudiment between 10 and 11 days' gestation. During the following few days of development there is a rapid inflow of stem cells to the rudiments. Since it is likely that stem cells, once they have entered the thymic primordium, are capable of only limited proliferation, it must be concluded that an inflow of stem cells continues once full lymphopoiesis has begun, although perhaps at a reduced rate. Finally, the importance of the interaction between stem cell and organ rudiment to normal thymic development is discussed in relation to the pathogenesis of thymic anomalies.

L3T4 effector cells in multiple organ-localized autoimmune disease in nude mice grafted with embryonic rat thymus.

“…One is the rat T cell population that was present in the thymic grafts and migrated into peripheral lymphoid tissues, while the other is mouse T cell population educated in the grafts . In the mouse, it is reported that lymphoid precursor cells first enter the fetal thymus at 10 .5 d of gestation (3) . The developmental stage of rat thymus is almost the same as that of mouse, or slightly behind.…”

Spatial, a gene expressed in thymic stromal cells, depends on three-dimensional thymus organization for its expression

“…The expression of Spatial in 10 day embryos slightly precedes the budding of the thymus and its initial seeding by HSC at about day 10.5 to day 11. 16,17,26 The timing of embryonic Spatial expression is coincident with the HSC seeding of the fetal liver from the yolk sac and para-aortic splanchnopleura which starts at around day 10, peaks at day 13 and then declines. 27,28 In fact, RT-PCR analysis of fetal tissues revealed that Spatial is also expressed in the 14 day fetal liver, but not in adult liver (Figure 6a).…”

“…Hematopoietic stem cell (HSC) seeding of the thymus begins at embryonic day 10 when waves of cells colonize the thymic rudiment while it is still attached to the pharyngeal pouch. [15][16][17] The products that attract HSC to the thymus are unknown but recent experiments have indicated that chemokines, integrins, and CD44 mediate the seeding of the thymus by HSC. [18][19][20] Upon entry into the thymus, HSC start to differentiate and the resulting daughter cells divide multiple times to a point where 95% of the thymus is composed of a transient population of lymphoid cells.…”

Tracing the first waves of lymphopoiesis in mice

“…The thymus rudiment is devoid of lympho-hematopoietic potentiality until ~E10.5 when an influx of progenitors begins (Owen and Ritter, 1969). GFP + cells, which were actually the first ones during embryonic development, became conspicuous both within and surrounding the thymus rudiment slightly later (Fig.…”