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Non-Hematopoietic and Hematopoietic SIRPα Signaling Differently Regulates Murine B Cell Maturation in Bone Marrow and Spleen.

Kolan SS, Lejon K, Koskinen Holm C, Sulniute R, Lundberg P, Matozaki T, Oldenborg PA - PLoS ONE (2015)

Bottom Line: Here we provide evidence that signal regulatory protein α (SIRPα), an Ig-superfamily ITIM-receptor expressed by myeloid but not by lymphoid cells, is involved in regulating B cell maturation.Lack of SIRPα signaling in adult SIRPα-mutant mice resulted in a reduced maturation of B cells in the bone marrow, evident by reduced numbers of semi-mature IgD+IgMhi follicular type-II (F-II) and mature IgD+IgMlo follicular type-I (F-I) B cells, as well as reduced blood B cell numbers.In addition, lack of SIRPα signaling also impaired follicular B cell maturation in the spleen.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Medical Biology, Umeå University, Umeå, Sweden.

ABSTRACT
B lymphocyte development occurs in the bone marrow, while final differentiation and maturation can occur in both the bone marrow and the spleen. Here we provide evidence that signal regulatory protein α (SIRPα), an Ig-superfamily ITIM-receptor expressed by myeloid but not by lymphoid cells, is involved in regulating B cell maturation. Lack of SIRPα signaling in adult SIRPα-mutant mice resulted in a reduced maturation of B cells in the bone marrow, evident by reduced numbers of semi-mature IgD+IgMhi follicular type-II (F-II) and mature IgD+IgMlo follicular type-I (F-I) B cells, as well as reduced blood B cell numbers. In addition, lack of SIRPα signaling also impaired follicular B cell maturation in the spleen. Maturing BM or splenic B cells of SIRPα-mutant mice were found to express higher levels of the pro-apoptotic protein BIM and apoptosis was increased among these B cells. Bone marrow reconstitution experiments revealed that the B cell maturation defect in bone marrow and blood was due to lack of SIRPα signaling in non-hematopoietic cells, while hematopoietic SIRPα signaling was important for follicular B cell maturation in the spleen. Adding on to our previous findings of a stromal cell defect in SIRPα-mutant mice was the finding that gene expression of receptor activator of nuclear factor-ĸB ligand (RANKL) was significantly lower in cultured bone marrow stromal cells of SIRPα mutant mice. These data suggest a novel and opposite contribution of SIRPα signaling within non-hematopoietic and hematopoietic cells, respectively, to maintain B cell maturation and to prevent apoptosis in the bone marrow and spleen of adult mice.

No MeSH data available.


Related in: MedlinePlus

Lack of SIRPα signaling in vivo results in reduced numbers of blood B cells.(A) Fraction of CD19+ blood B cells in 12 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). (B) CD19+ blood B cell subsets were separated based on their expression levels of sIgM and CD23 to identify sIgMhiCD23-/lo immature B cells (Immature B), sIgMhiCD23hi semi-mature/follicular type-II (F-II B) B cells and sIgMlo/intCD23hi mature/F-I (Mature B) B cells. Data shown are the numbers of total CD19+, immature, F-II, or mature B cells per microliter of blood in wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars) at (C) 12 weeks or (D) 20 weeks of age. Data are means±SEM for 9 mice/group at 12 weeks and 4–7 mice/group at 20 weeks of age. (E) Absolute numbers of CD4/8+ T cells, CD11bhi Gr1hi neutrophils and CD11bhi Gr1low monocytes per microliter of blood in 16 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). Data are means±SEM for 5 mice/group. *P<0.05 and **P<0.01, as compared with that in wild-type mice, using Student’s t-test for unpaired analyses.
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pone.0134113.g001: Lack of SIRPα signaling in vivo results in reduced numbers of blood B cells.(A) Fraction of CD19+ blood B cells in 12 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). (B) CD19+ blood B cell subsets were separated based on their expression levels of sIgM and CD23 to identify sIgMhiCD23-/lo immature B cells (Immature B), sIgMhiCD23hi semi-mature/follicular type-II (F-II B) B cells and sIgMlo/intCD23hi mature/F-I (Mature B) B cells. Data shown are the numbers of total CD19+, immature, F-II, or mature B cells per microliter of blood in wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars) at (C) 12 weeks or (D) 20 weeks of age. Data are means±SEM for 9 mice/group at 12 weeks and 4–7 mice/group at 20 weeks of age. (E) Absolute numbers of CD4/8+ T cells, CD11bhi Gr1hi neutrophils and CD11bhi Gr1low monocytes per microliter of blood in 16 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). Data are means±SEM for 5 mice/group. *P<0.05 and **P<0.01, as compared with that in wild-type mice, using Student’s t-test for unpaired analyses.

Mentions: We have previously found that the proportion of blood B cells out of total lymphocytes was similar in 6–12 weeks old wild-type and SIRPα-mutant mice [24]. We confirmed this in blood of 12 weeks old wild-type and SIRPα-mutant mice (48.5±1.8% vs. 47.1±0.7%, respectively; P>0.05) (Fig 1A). However, the absolute number of CD19+ B cells was reduced by 30%, as compared with that in age-matched wild-type mice (P<0.05, Fig 1C). The discrepancy between a normal B cell frequency and reduced absolute B cell numbers can be explained by the fact that the absolute number of blood T cells was reduced by about 33% in SIRPα-mutant mice (Fig 1E). Since the CD19+ blood B cell population contains several separate B cell subsets at different stages of their maturation, we also labeled blood cells with mAbs against sIgM and CD23 to enable identification of sIgMhiCD23-/lo immature B cells, sIgMhiCD23hi semi-mature/follicular type-II B cells and sIgMlo/intCD23hi mature/follicular type-I B cells (Fig 1B). In 12 weeks old SIRPα-mutants, all three B cell subsets were significantly reduced (43%, 45% and 30%, respectively), as compared with that in wild-type mice (Fig 1C). This blood B cell deficit of SIRPα-mutant mice was further enhanced at 20 weeks of age (Fig 1D). To investigate if SIRPα-mutant mice also had a reduced number of myeloid lineage cells in the blood, we quantified the numbers of neutrophils and monocytes in blood of 16 weeks old wild-type or SIRPα-mutant mice. This analysis revealed no differences among neutrophils or monocytes in the two genotypes of mice (Fig 1E). Thus, lack of SIRPα signaling appeared to be of importance to maintain normal numbers of circulating B cells in adult mice.


Non-Hematopoietic and Hematopoietic SIRPα Signaling Differently Regulates Murine B Cell Maturation in Bone Marrow and Spleen.

Kolan SS, Lejon K, Koskinen Holm C, Sulniute R, Lundberg P, Matozaki T, Oldenborg PA - PLoS ONE (2015)

Lack of SIRPα signaling in vivo results in reduced numbers of blood B cells.(A) Fraction of CD19+ blood B cells in 12 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). (B) CD19+ blood B cell subsets were separated based on their expression levels of sIgM and CD23 to identify sIgMhiCD23-/lo immature B cells (Immature B), sIgMhiCD23hi semi-mature/follicular type-II (F-II B) B cells and sIgMlo/intCD23hi mature/F-I (Mature B) B cells. Data shown are the numbers of total CD19+, immature, F-II, or mature B cells per microliter of blood in wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars) at (C) 12 weeks or (D) 20 weeks of age. Data are means±SEM for 9 mice/group at 12 weeks and 4–7 mice/group at 20 weeks of age. (E) Absolute numbers of CD4/8+ T cells, CD11bhi Gr1hi neutrophils and CD11bhi Gr1low monocytes per microliter of blood in 16 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). Data are means±SEM for 5 mice/group. *P<0.05 and **P<0.01, as compared with that in wild-type mice, using Student’s t-test for unpaired analyses.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4519279&req=5

pone.0134113.g001: Lack of SIRPα signaling in vivo results in reduced numbers of blood B cells.(A) Fraction of CD19+ blood B cells in 12 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). (B) CD19+ blood B cell subsets were separated based on their expression levels of sIgM and CD23 to identify sIgMhiCD23-/lo immature B cells (Immature B), sIgMhiCD23hi semi-mature/follicular type-II (F-II B) B cells and sIgMlo/intCD23hi mature/F-I (Mature B) B cells. Data shown are the numbers of total CD19+, immature, F-II, or mature B cells per microliter of blood in wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars) at (C) 12 weeks or (D) 20 weeks of age. Data are means±SEM for 9 mice/group at 12 weeks and 4–7 mice/group at 20 weeks of age. (E) Absolute numbers of CD4/8+ T cells, CD11bhi Gr1hi neutrophils and CD11bhi Gr1low monocytes per microliter of blood in 16 weeks old wild-type (Wt–open bars) or SIRPα-mutant mice (Mut–black bars). Data are means±SEM for 5 mice/group. *P<0.05 and **P<0.01, as compared with that in wild-type mice, using Student’s t-test for unpaired analyses.
Mentions: We have previously found that the proportion of blood B cells out of total lymphocytes was similar in 6–12 weeks old wild-type and SIRPα-mutant mice [24]. We confirmed this in blood of 12 weeks old wild-type and SIRPα-mutant mice (48.5±1.8% vs. 47.1±0.7%, respectively; P>0.05) (Fig 1A). However, the absolute number of CD19+ B cells was reduced by 30%, as compared with that in age-matched wild-type mice (P<0.05, Fig 1C). The discrepancy between a normal B cell frequency and reduced absolute B cell numbers can be explained by the fact that the absolute number of blood T cells was reduced by about 33% in SIRPα-mutant mice (Fig 1E). Since the CD19+ blood B cell population contains several separate B cell subsets at different stages of their maturation, we also labeled blood cells with mAbs against sIgM and CD23 to enable identification of sIgMhiCD23-/lo immature B cells, sIgMhiCD23hi semi-mature/follicular type-II B cells and sIgMlo/intCD23hi mature/follicular type-I B cells (Fig 1B). In 12 weeks old SIRPα-mutants, all three B cell subsets were significantly reduced (43%, 45% and 30%, respectively), as compared with that in wild-type mice (Fig 1C). This blood B cell deficit of SIRPα-mutant mice was further enhanced at 20 weeks of age (Fig 1D). To investigate if SIRPα-mutant mice also had a reduced number of myeloid lineage cells in the blood, we quantified the numbers of neutrophils and monocytes in blood of 16 weeks old wild-type or SIRPα-mutant mice. This analysis revealed no differences among neutrophils or monocytes in the two genotypes of mice (Fig 1E). Thus, lack of SIRPα signaling appeared to be of importance to maintain normal numbers of circulating B cells in adult mice.

Bottom Line: Here we provide evidence that signal regulatory protein α (SIRPα), an Ig-superfamily ITIM-receptor expressed by myeloid but not by lymphoid cells, is involved in regulating B cell maturation.Lack of SIRPα signaling in adult SIRPα-mutant mice resulted in a reduced maturation of B cells in the bone marrow, evident by reduced numbers of semi-mature IgD+IgMhi follicular type-II (F-II) and mature IgD+IgMlo follicular type-I (F-I) B cells, as well as reduced blood B cell numbers.In addition, lack of SIRPα signaling also impaired follicular B cell maturation in the spleen.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Medical Biology, Umeå University, Umeå, Sweden.

ABSTRACT
B lymphocyte development occurs in the bone marrow, while final differentiation and maturation can occur in both the bone marrow and the spleen. Here we provide evidence that signal regulatory protein α (SIRPα), an Ig-superfamily ITIM-receptor expressed by myeloid but not by lymphoid cells, is involved in regulating B cell maturation. Lack of SIRPα signaling in adult SIRPα-mutant mice resulted in a reduced maturation of B cells in the bone marrow, evident by reduced numbers of semi-mature IgD+IgMhi follicular type-II (F-II) and mature IgD+IgMlo follicular type-I (F-I) B cells, as well as reduced blood B cell numbers. In addition, lack of SIRPα signaling also impaired follicular B cell maturation in the spleen. Maturing BM or splenic B cells of SIRPα-mutant mice were found to express higher levels of the pro-apoptotic protein BIM and apoptosis was increased among these B cells. Bone marrow reconstitution experiments revealed that the B cell maturation defect in bone marrow and blood was due to lack of SIRPα signaling in non-hematopoietic cells, while hematopoietic SIRPα signaling was important for follicular B cell maturation in the spleen. Adding on to our previous findings of a stromal cell defect in SIRPα-mutant mice was the finding that gene expression of receptor activator of nuclear factor-ĸB ligand (RANKL) was significantly lower in cultured bone marrow stromal cells of SIRPα mutant mice. These data suggest a novel and opposite contribution of SIRPα signaling within non-hematopoietic and hematopoietic cells, respectively, to maintain B cell maturation and to prevent apoptosis in the bone marrow and spleen of adult mice.

No MeSH data available.


Related in: MedlinePlus