Key Molecule That Keeps Immune Cell Development On Track Described

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In the latest issue of Nature, researchers at the Perelman School of Medicine at the University of Pennsylvania clarify the role of two proteins key to T-cell development. They found that one well-known protein called Notch passes off much of its role during T-cell maturation to another protein called TCF-1. T cells are required for many aspects of immunity, and understanding how these proteins influence the production of infection-fighting cells could improve treatments for immune-suppressed patients.8 `' k5 \& D3 r* ?  l4 f
    The research group, led by senior author Avinash Bhandoola, MBBS, PhD, associate professor of Pathology and Laboratory Medicine, found an important role in early T-cell development for T-cell factor 1 (TCF-1), which is turned on by Notch signals." w& Z. H; n/ P& J: x' O
    "Notch triggers the process of T-cell development, and turns on expression of TCF-1, but Notch itself doesn't stick around; it's more of a kiss-and-run molecule," says Bhandoola. In contrast, once induced by Notch, TCF-1 is faithfully expressed throughout T-cell maturation.
* X) N* n* J9 [2 H+ p3 {; E4 T: ?/ a    T cells are made in the thymus, a small organ situated under the breastbone near the heart. However, T cells, like all blood-cell types, originate from blood-producing stem cells in the bone marrow. Immature T-cell progenitors leave the bone marrow, settle within the thymus, and eventually give rise to T cells.* A# r4 |9 x* H
    Notch regulates cell-fate decisions in many cell types in addition to immune cells. Past work at Penn helped demonstrate that Notch is active in early T-cell progenitors in the thymus of mice, and drives the differentiation of these progenitors down the T cell pathway.
* k8 I+ I3 }! U1 r' |    Co-first authors, Anthony Wei-Shin Chi, MD, PhD, and Brittany Nicole Weber, BS, were graduate students together in the Bhandoola lab. They used retroviruses to express TCF-1 in immature blood progenitor cells. "If you expose progenitor cells to Notch signals in culture, we know that they will express TCF-1 and take on other features of T cells," says Chi.
& U7 U+ M. x3 H0 w; }( L1 u    However, when they forced expression of TCF-1 in cells using retroviruses, Weber noticed expression of T-cell proteins on the surface of cells -- even when Notch signals were absent. The team further characterized these new T-lineage cells by looking at gene expression on microarrays and found they expressed many T-cell specific genes. They concluded that Notch normally turns on TCF-1 early in development, and that TCF-1 then does the job of turning on T-cell genes and keeps T-cell maturation on the right track.  Z) |% t: O: J, y4 f7 X
    "The data are telling us that Notch delegates much of its work during T-cell development to TCF-1," says Bhandoola, "But we now have many questions about what comes next."
/ l' V  b1 _) p1 |/ M2 h    Adds Weber, "Some of the new questions are: How is TCF-1 regulated after Notch steps off stage? What keeps it on? What is TCF-1 doing? And how is it doing it?"
7 p& U! |" F* \, CIn many clinical settings, early T-cell progenitors are likely to be deficient, especially in patients undergoing bone marrow or blood-cell-producing stem cell transplantation -- situations in which new T cells fail to be produced for long periods of time. In some patients, especially elderly ones, there is never true recovery of T cells, and this non-recovery can be associated with infection.8 ~) \. A  _8 @
    "To improve the outcome of transplant patients, the process of T-cell development needs to be better understood," says Chi. This may also be important in cancer patients who get profound immunosuppression from treatments and in AIDS patients when T cells are not made at a rate sufficient to replenish the T-cell pool.
1 {; h, f+ R# J9 V    "It's possible that one day we will use molecules like TCF-1 to improve T-cell development for people," says Weber.
+ p/ {( A. `2 m: l: Q' E  `    The work was supported by grants from the National Institute of Allergy and Infectious Diseases and from the Leukemia and Lymphoma Society.
+ Q; g: t! @. ?& _- ?- {    Other co-authors, all from Penn, are Alejandro Chavez, Yumi Yashiro-Ohtani, Qi Yang, and Olga Shestova.

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