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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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Immunohistochemistry of splenic B cells in an adult Syk−/− mouse. Sections were stained with antibodies to IgD or IgM; these were revealed with peroxidase (brown) or with antibodies to CD3 or B220 revealed with alkaline phosphatase (blue) as indicated. Sections labeled “none” were  stained only with the peroxidase-coupled secondary antibody to reveal endogenous peroxidase activity. (a–c) Serial sections from the spleen of an exceptional Syk−/− mouse that survived to adulthood; small numbers of B220+ cells are found in the outer T zone (T) and a proportion of these are IgM+ (arrows in b), but none are IgD+ nor have they entered the follicles. The B220+IgM− cells in this spleen were shown to be CD3− (data not shown). Note in  c the brown staining of eosinophils which contain endogenous peroxidase activity; the same eosinophils are seen staining brown in a and b. (d–f ) Serial sections from a heterozygous littermate showing the development of normal follicles (F), which contain IgM+IgD+ recirculating B cells; IgM+IgD− plasma  cells are present in extra-follicular foci (E) in this spleen. Scale: black bar represents 100 μm. Analysis of a second Syk−/− mouse gave similar results.
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Figure 1: Immunohistochemistry of splenic B cells in an adult Syk−/− mouse. Sections were stained with antibodies to IgD or IgM; these were revealed with peroxidase (brown) or with antibodies to CD3 or B220 revealed with alkaline phosphatase (blue) as indicated. Sections labeled “none” were stained only with the peroxidase-coupled secondary antibody to reveal endogenous peroxidase activity. (a–c) Serial sections from the spleen of an exceptional Syk−/− mouse that survived to adulthood; small numbers of B220+ cells are found in the outer T zone (T) and a proportion of these are IgM+ (arrows in b), but none are IgD+ nor have they entered the follicles. The B220+IgM− cells in this spleen were shown to be CD3− (data not shown). Note in c the brown staining of eosinophils which contain endogenous peroxidase activity; the same eosinophils are seen staining brown in a and b. (d–f ) Serial sections from a heterozygous littermate showing the development of normal follicles (F), which contain IgM+IgD+ recirculating B cells; IgM+IgD− plasma cells are present in extra-follicular foci (E) in this spleen. Scale: black bar represents 100 μm. Analysis of a second Syk−/− mouse gave similar results.

Mentions: We had earlier shown, using irradiated mice reconstituted with Syk−/− fetal liver, that there was a partial block at the pro-B to pre-B cell transition, suggestive of a role for Syk in pre-BCR signaling (23). Furthermore, we noted that despite the presence of a small number of immature Syk−/− B cells in the marrow, no detectable recirculating B cells accumulated in the peripheral lymphoid organs, at least as judged by flow cytometric analysis (23). To investigate further the fate of Syk−/− immature B cells, we turned to the more sensitive technique of immunohistology to look for the presence of Syk−/− B lineage cells in the spleen, since this is at least one of the sites to which immature B cells migrate upon leaving the marrow (3, 4). Initially, analysis was performed on spleens of two Syk−/− mice that, exceptionally, had survived to adulthood. Strikingly, this showed small numbers of immature (IgM+IgD−) B cells lined up along the edge of the T zone, but a total absence of both follicles and recirculating (IgM+IgD+) B cells (Fig. 1). Thus Syk−/− immature B cells migrate from the marrow to the spleen but do not mature into recirculating follicular B cells.


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)

Immunohistochemistry of splenic B cells in an adult Syk−/− mouse. Sections were stained with antibodies to IgD or IgM; these were revealed with peroxidase (brown) or with antibodies to CD3 or B220 revealed with alkaline phosphatase (blue) as indicated. Sections labeled “none” were  stained only with the peroxidase-coupled secondary antibody to reveal endogenous peroxidase activity. (a–c) Serial sections from the spleen of an exceptional Syk−/− mouse that survived to adulthood; small numbers of B220+ cells are found in the outer T zone (T) and a proportion of these are IgM+ (arrows in b), but none are IgD+ nor have they entered the follicles. The B220+IgM− cells in this spleen were shown to be CD3− (data not shown). Note in  c the brown staining of eosinophils which contain endogenous peroxidase activity; the same eosinophils are seen staining brown in a and b. (d–f ) Serial sections from a heterozygous littermate showing the development of normal follicles (F), which contain IgM+IgD+ recirculating B cells; IgM+IgD− plasma  cells are present in extra-follicular foci (E) in this spleen. Scale: black bar represents 100 μm. Analysis of a second Syk−/− mouse gave similar results.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2199169&req=5

Figure 1: Immunohistochemistry of splenic B cells in an adult Syk−/− mouse. Sections were stained with antibodies to IgD or IgM; these were revealed with peroxidase (brown) or with antibodies to CD3 or B220 revealed with alkaline phosphatase (blue) as indicated. Sections labeled “none” were stained only with the peroxidase-coupled secondary antibody to reveal endogenous peroxidase activity. (a–c) Serial sections from the spleen of an exceptional Syk−/− mouse that survived to adulthood; small numbers of B220+ cells are found in the outer T zone (T) and a proportion of these are IgM+ (arrows in b), but none are IgD+ nor have they entered the follicles. The B220+IgM− cells in this spleen were shown to be CD3− (data not shown). Note in c the brown staining of eosinophils which contain endogenous peroxidase activity; the same eosinophils are seen staining brown in a and b. (d–f ) Serial sections from a heterozygous littermate showing the development of normal follicles (F), which contain IgM+IgD+ recirculating B cells; IgM+IgD− plasma cells are present in extra-follicular foci (E) in this spleen. Scale: black bar represents 100 μm. Analysis of a second Syk−/− mouse gave similar results.
Mentions: We had earlier shown, using irradiated mice reconstituted with Syk−/− fetal liver, that there was a partial block at the pro-B to pre-B cell transition, suggestive of a role for Syk in pre-BCR signaling (23). Furthermore, we noted that despite the presence of a small number of immature Syk−/− B cells in the marrow, no detectable recirculating B cells accumulated in the peripheral lymphoid organs, at least as judged by flow cytometric analysis (23). To investigate further the fate of Syk−/− immature B cells, we turned to the more sensitive technique of immunohistology to look for the presence of Syk−/− B lineage cells in the spleen, since this is at least one of the sites to which immature B cells migrate upon leaving the marrow (3, 4). Initially, analysis was performed on spleens of two Syk−/− mice that, exceptionally, had survived to adulthood. Strikingly, this showed small numbers of immature (IgM+IgD−) B cells lined up along the edge of the T zone, but a total absence of both follicles and recirculating (IgM+IgD+) B cells (Fig. 1). Thus Syk−/− immature B cells migrate from the marrow to the spleen but do not mature into recirculating follicular B cells.

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