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Syk tyrosine kinase is required for the positive selection of immature B cells into the recirculating B cell pool.

Turner M, Gulbranson-Judge A, Quinn ME, Walters AE, MacLennan IC, Tybulewicz VL - J. Exp. Med. (1997)

Bottom Line: Despite this defect in maturation, Syk-deficient B cells were seen to give rise to switched as well as nonswitched splenic plasma cells.Normally only a proportion of immature B cells is recruited into the recirculating pool.Our results suggest that Syk transduces a BCR signal that is absolutely required for the positive selection of immature B cells into the recirculating B cell pool.

View Article: PubMed Central - PubMed

Affiliation: National Institute for Medical Research, Mill Hill, London, NW7 1AA, United Kingdom.

ABSTRACT
The tyrosine kinase Syk has been implicated as a key signal transducer from the B cell antigen receptor (BCR). We show here that mutation of the Syk gene completely blocks the maturation of immature B cells into recirculating cells and stops their entry into B cell follicles. Furthermore, using radiation chimeras we demonstrate that this developmental block is due to the absence of Syk in the B cells themselves. Syk-deficient B cells are shown to have the life span of normal immature B cells. If this is extended by over-expression of Bcl-2, they accumulate in the T zone and red pulp of the spleen in increased numbers, but still fail to mature to become recirculating follicular B cells. Despite this defect in maturation, Syk-deficient B cells were seen to give rise to switched as well as nonswitched splenic plasma cells. Normally only a proportion of immature B cells is recruited into the recirculating pool. Our results suggest that Syk transduces a BCR signal that is absolutely required for the positive selection of immature B cells into the recirculating B cell pool.

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Life span of Syk−/− immature B cells is increased by expression of Bcl-2. Chimeric mice reconstituted with Syk−/−/3-83 fetal livers  with and without Bcl-2Tg were given a 12-h pulse of BrdU. Graph shows  the percentage of splenic 3-83+ B cells that were also labeled with BrdU  either 4 or 8 d after the BrdU pulse. At each time point, spleens from  three or four mice were analyzed by quantitative immunohistology as  previously described (4). The lines are drawn between median values.  The number of cells enumerated was 168–263 cells/spleen in the Syk−/−/ 3-83 chimeras and 673–994 cells/spleen in the Syk−/−/3-83/Bcl-2Tg chimeras.
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Figure 4: Life span of Syk−/− immature B cells is increased by expression of Bcl-2. Chimeric mice reconstituted with Syk−/−/3-83 fetal livers with and without Bcl-2Tg were given a 12-h pulse of BrdU. Graph shows the percentage of splenic 3-83+ B cells that were also labeled with BrdU either 4 or 8 d after the BrdU pulse. At each time point, spleens from three or four mice were analyzed by quantitative immunohistology as previously described (4). The lines are drawn between median values. The number of cells enumerated was 168–263 cells/spleen in the Syk−/−/ 3-83 chimeras and 673–994 cells/spleen in the Syk−/−/3-83/Bcl-2Tg chimeras.

Mentions: To confirm that the Bcl-2Tg had indeed increased the life-span of Syk-deficient immature B cells, Syk−/−/3-83 chimeras with and without Bcl-2Tg were given a 12-h pulse with the thymidine analogue BrdU to identify cells proliferating during the pulse that had subsequently gone out of cell cycle. Pre-B cells exit the cell cycle ∼24 h before first expressing surface immunoglobulin (35) and immature and recirculating B cells do not subsequently proliferate unless they are recruited into an antibody response (4). In wild-type rodents, pulse-labeled immature B cells enter the spleen on the second and third day after a 12-h BrdU pulse and are lost within 7 d (4, 36). In this experiment, spleens of the chimeric mice were examined 4 and 8 d after the BrdU pulse. At 4 d, BrdU-labeled 3-83+ B cells were present in roughly equal proportions in mice with and without Bcl-2Tg (Fig. 4). By 8 d, as expected, BrdU-labeled B cells were largely absent from the chimeras without the Bcl-2Tg (Fig. 2 d) but were present in an undiminished proportion of the B cells carrying the Bcl-2Tg (Fig. 2 e). Thus, in the absence of Bcl-2Tg, Syk−/− immature cells turn over with normal kinetics. However, in chimeras with Bcl-2Tg, the life span of Syk-deficient immature B cells was significantly extended.


Syk tyrosine kinase is required for the positive selection of immature B cells into the recirculating B cell pool.

Turner M, Gulbranson-Judge A, Quinn ME, Walters AE, MacLennan IC, Tybulewicz VL - J. Exp. Med. (1997)

Life span of Syk−/− immature B cells is increased by expression of Bcl-2. Chimeric mice reconstituted with Syk−/−/3-83 fetal livers  with and without Bcl-2Tg were given a 12-h pulse of BrdU. Graph shows  the percentage of splenic 3-83+ B cells that were also labeled with BrdU  either 4 or 8 d after the BrdU pulse. At each time point, spleens from  three or four mice were analyzed by quantitative immunohistology as  previously described (4). The lines are drawn between median values.  The number of cells enumerated was 168–263 cells/spleen in the Syk−/−/ 3-83 chimeras and 673–994 cells/spleen in the Syk−/−/3-83/Bcl-2Tg chimeras.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2199169&req=5

Figure 4: Life span of Syk−/− immature B cells is increased by expression of Bcl-2. Chimeric mice reconstituted with Syk−/−/3-83 fetal livers with and without Bcl-2Tg were given a 12-h pulse of BrdU. Graph shows the percentage of splenic 3-83+ B cells that were also labeled with BrdU either 4 or 8 d after the BrdU pulse. At each time point, spleens from three or four mice were analyzed by quantitative immunohistology as previously described (4). The lines are drawn between median values. The number of cells enumerated was 168–263 cells/spleen in the Syk−/−/ 3-83 chimeras and 673–994 cells/spleen in the Syk−/−/3-83/Bcl-2Tg chimeras.
Mentions: To confirm that the Bcl-2Tg had indeed increased the life-span of Syk-deficient immature B cells, Syk−/−/3-83 chimeras with and without Bcl-2Tg were given a 12-h pulse with the thymidine analogue BrdU to identify cells proliferating during the pulse that had subsequently gone out of cell cycle. Pre-B cells exit the cell cycle ∼24 h before first expressing surface immunoglobulin (35) and immature and recirculating B cells do not subsequently proliferate unless they are recruited into an antibody response (4). In wild-type rodents, pulse-labeled immature B cells enter the spleen on the second and third day after a 12-h BrdU pulse and are lost within 7 d (4, 36). In this experiment, spleens of the chimeric mice were examined 4 and 8 d after the BrdU pulse. At 4 d, BrdU-labeled 3-83+ B cells were present in roughly equal proportions in mice with and without Bcl-2Tg (Fig. 4). By 8 d, as expected, BrdU-labeled B cells were largely absent from the chimeras without the Bcl-2Tg (Fig. 2 d) but were present in an undiminished proportion of the B cells carrying the Bcl-2Tg (Fig. 2 e). Thus, in the absence of Bcl-2Tg, Syk−/− immature cells turn over with normal kinetics. However, in chimeras with Bcl-2Tg, the life span of Syk-deficient immature B cells was significantly extended.

Bottom Line: Despite this defect in maturation, Syk-deficient B cells were seen to give rise to switched as well as nonswitched splenic plasma cells.Normally only a proportion of immature B cells is recruited into the recirculating pool.Our results suggest that Syk transduces a BCR signal that is absolutely required for the positive selection of immature B cells into the recirculating B cell pool.

View Article: PubMed Central - PubMed

Affiliation: National Institute for Medical Research, Mill Hill, London, NW7 1AA, United Kingdom.

ABSTRACT
The tyrosine kinase Syk has been implicated as a key signal transducer from the B cell antigen receptor (BCR). We show here that mutation of the Syk gene completely blocks the maturation of immature B cells into recirculating cells and stops their entry into B cell follicles. Furthermore, using radiation chimeras we demonstrate that this developmental block is due to the absence of Syk in the B cells themselves. Syk-deficient B cells are shown to have the life span of normal immature B cells. If this is extended by over-expression of Bcl-2, they accumulate in the T zone and red pulp of the spleen in increased numbers, but still fail to mature to become recirculating follicular B cells. Despite this defect in maturation, Syk-deficient B cells were seen to give rise to switched as well as nonswitched splenic plasma cells. Normally only a proportion of immature B cells is recruited into the recirculating pool. Our results suggest that Syk transduces a BCR signal that is absolutely required for the positive selection of immature B cells into the recirculating B cell pool.

Show MeSH
Related in: MedlinePlus