Hemopoiesis in the Thymus

Kendall, Marion D.

doi:10.1155/1995/69454

Cited by 22 publications

(21 citation statements)

References 53 publications

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“…CCX-CKR1 expression is restricted to TECs ensheathing the blood vessels of the medulla, the corticomedullary junction, and to subcapsular zone TECs. This expression pattern overlaps but is not identical with the location of type I epithelium that has been classified on the basis of ultrastructural analyses (30)(31)(32), because type I epithelial cells ensheathing cortical blood vessels are CCX-CKR1-negative. CCX-CKR1 marks the thymic niche to which hematopoietic precursors are recruited from the blood.…”

Section: Discussionmentioning

confidence: 84%

A silent chemokine receptor regulates steady-state leukocyte homing in vivo

Heinzel

Benz

Bleul

2007

Proc. Natl. Acad. Sci. U.S.A.

146

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The location of leukocytes in different microenvironments is intimately connected to their function and, in the case of leukocyte precursors, to the executed differentiation and maturation program. Leukocyte migration within lymphoid organs has been shown to be mediated by constitutively expressed chemokines, but how the bioavailability of these homeostatic chemokines is regulated remains unknown. Here, we report in vivo evidence for the role of a nonsignaling chemokine receptor in the migration of leukocytes under physiological, i.e., noninflammatory, conditions. We have studied the in vivo role of the silent chemokine receptor CCX-CKR1 by both loss-and gain-of-function approaches. CCX-CKR1 binds the constitutively expressed chemokines CC chemokine ligand (CCL)19, CCL21, and CCL25. We find that CCX-CKR1 is involved in the steady-state homing of CD11c ؉ MHCII high dendritic cells to skin-draining lymph nodes, and it affects the homing of embryonic thymic precursors to the thymic anlage. These observations indicate that the silent chemokine receptor CCX-CKR1, which is exclusively expressed by stroma cells, but not hematopoietic cells themselves, regulates homeostatic leukocyte migration by controlling the availability of chemokines in the extracellular space. This finding adds another level of complexity to our understanding of leukocyte homeostatic migration.cell trafficking ͉ homeostasis ͉ lymphopoiesis ͉ thymus

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Section: Discussionmentioning

confidence: 84%

A silent chemokine receptor regulates steady-state leukocyte homing in vivo

Heinzel

Benz

Bleul

2007

Proc. Natl. Acad. Sci. U.S.A.

146

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“…suppression of red blood cell production or blood loss), typically peaks at 4-7 days, and gradually declines within 2-3 weeks of the original insult (Fernandez and Grindem, 2006). To our knowledge, our study is the first to examine changes in proportion of reticulocytes across the reproductive cycle, although previous studies have investigated changes in the hematopoietic organs in this context (reviewed by Kendall, 1995;Kalmbach et al, 2004). For example, Jones (Jones, 1983) documented that the thymus became enlarged and actively produced red blood cells in the redbilled quelea (Quelea quelea) during incubation, and suggested that this functioned to augment erythropoiesis in the bone marrow and compensate for anemia during egg-laying.…”

Section: Discussionmentioning

confidence: 95%

Hematological changes associated with egg production: direct evidence for changes in erythropoiesis but a lack of resource dependence?

Wagner

Stables

Williams

2008

Journal of Experimental Biology

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SUMMARYReductions in hematological parameters among laying birds are well reported, but the cause of this anemia is not known. We tested specific predictions generated from several, non-mutually exclusive hypotheses for mechanisms underlying reproductive anemia associated with egg production (hemodilution, transient suppression of erythropoiesis, resource dependence) in relation to (1) the time-course of development and recovery from anemia, (2) changes in specific hematological traits, and (3) the effect of diet quality, in female zebra finches (Taeniopygia guttata). Female zebra finches showed marked decreases in hematocrit (~6%), red blood cell counts (~8%), and plasma hemoglobin concentration (~9%) during egg production, even on a high-quality ad libitum diet, consistent with an effect of hemodilution associated with yolk precursor production. However, our results provide strong support for the hypothesis that erythropoiesis is transiently suppressed during egg-laying and that the recovery from anemia is relatively long-lasting, extending through incubation and hatching periods. Decreased hematocrit, red blood cell counts, and hemoglobin concentration did not recover at clutch completion, but showed evidence of recovery to baseline pre-breeding levels at hatching. More importantly, there was significant time-dependent variation in the proportion of reticulocytes, which increased at clutch completion but peaked at hatching 10-12 days after clutch completion, and in mean red blood cell volume, which showed a significant increase at clutch completion; consistent with enhanced production and release of larger immature cells into the circulation following suppression of erythropoiesis. Finally, we found no evidence for resource dependence of anemia associated with egg production in relation to diet quality, i.e. exogenous lipid and protein resources available to the laying female. This study demonstrates that transient suppression of erythropoiesis and, subsequently, increased reticulocytosis, are key components of reproductive anemia in egg-laying females.

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“…A variable amount of intrathymic MCs has been reported during embryogenesis in different species (Bodey et al 1998). This finding has not stimulated any interpretative effort, being merely considered a secondary phenomenon related to a certain degree of hematopoiesis that occurs in this organ in the early stages of development (Kendall 1995;Kendall et al 1999). However, the high number of MCs observed in the chick embryo thymus-coupled with the ultrastructural features of MC degranulation and the close relationship between MCs and the extracellular matrixdeserves special attention and suggests some possible, still unknown, MC functions during thymic organogenesis.…”

Section: Discussionmentioning

confidence: 99%

“…Sporadic studies have reported on MC localization to embryonic thymus, and data have been related to a certain degree of hematopoiesis that occurs in this organ during embryogenesis (Bodey et al 1998;Kendall 1995;Kendall et al 1999). In the present study, we investigated by transmission electron microscopy the rich population of MCs in the chicken thymus during embryonic life.…”

Section: Introductionmentioning

confidence: 99%

The thymus is a site of mast cell development in chicken embryos

et al. 2004

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Thymic mast cells were studied by light and transmission electron microscopy in chicken embryos during organogenesis. Mast cells made their first appearance at day 15. At days 16 and 17, there was a burst of mast cell development with a peak of 278 +/- 54 cells/mm(2) at day 16. Then, mast cell density decreased until hatching. During the whole embryonic period, about 80% of mast cells localized to the thymic medulla. In the cortex, they were less numerous, and some rare mast cells could be identified in the capsule and septa. Thymic mast cells could be recognized in association with hematopoietic foci, but frequently they grew independently from areas of hematopoiesis and appeared as single cells interspersed among thymocytes, thymic epithelial cells, and interdigitating cells. They were often recognized in close relationship with the scanty and delicate extracellular matrix of the developing gland. Viewed by electron microscopy, mast cells were relatively small cells, with a few secretory granules. Exocytosis was never seen, but, notably, granules emptied in a piecemeal degranulation fashion. This study demonstrates that the chicken thymus is a site of mast cell development during embryogenesis. The high mast cell density we found suggests a possible role for these cells during thymus organogenesis.

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Hemopoiesis in the Thymus

Cited by 22 publications

References 53 publications

A silent chemokine receptor regulates steady-state leukocyte homing in vivo

A silent chemokine receptor regulates steady-state leukocyte homing in vivo

Hematological changes associated with egg production: direct evidence for changes in erythropoiesis but a lack of resource dependence?

The thymus is a site of mast cell development in chicken embryos

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