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IL-21 acts directly on B cells to regulate Bcl-6 expression and germinal center responses.

Linterman MA, Beaton L, Yu D, Ramiscal RR, Srivastava M, Hogan JJ, Verma NK, Smyth MJ, Rigby RJ, Vinuesa CG - J. Exp. Med. (2010)

Bottom Line: To date, it is unclear whether the effect of IL-21 on GC formation is predominantly a consequence of this cytokine acting directly on the Tfh cells or if IL-21 directly influences GC B cells.IL-21 deficiency profoundly impaired affinity maturation and reduced the proportion of IgG1(+) GC B cells but did not affect formation of early memory B cells.In contrast to the requirement for IL-21 in the follicular response to sheep red blood cells, a purely extrafollicular antibody response to Salmonella dominated by IgG2a was intact in the absence of IL-21.

View Article: PubMed Central - HTML - PubMed

Affiliation: John Curtin School of Medical Research, Australian National University, Canberra, ACT 2601, Australia.

ABSTRACT
During T cell-dependent responses, B cells can either differentiate extrafollicularly into short-lived plasma cells or enter follicles to form germinal centers (GCs). Interactions with T follicular helper (Tfh) cells are required for GC formation and for selection of somatically mutated GC B cells. Interleukin (IL)-21 has been reported to play a role in Tfh cell formation and in B cell growth, survival, and isotype switching. To date, it is unclear whether the effect of IL-21 on GC formation is predominantly a consequence of this cytokine acting directly on the Tfh cells or if IL-21 directly influences GC B cells. We show that IL-21 acts in a B cell-intrinsic fashion to control GC B cell formation. Mixed bone marrow chimeras identified a significant B cell-autonomous effect of IL-21 receptor (R) signaling throughout all stages of the GC response. IL-21 deficiency profoundly impaired affinity maturation and reduced the proportion of IgG1(+) GC B cells but did not affect formation of early memory B cells. IL-21R was required on GC B cells for maximal expression of Bcl-6. In contrast to the requirement for IL-21 in the follicular response to sheep red blood cells, a purely extrafollicular antibody response to Salmonella dominated by IgG2a was intact in the absence of IL-21.

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Lack of IL-21R signaling reduces the expression of Bcl-6 in GC B cells. (A) Flow cytometric contour plots indicating the gating strategy for non-GC and GC B220+ cells (left) and BCL-6 expression on GL-7+ (middle) and Fas+ (right) B cells. (B and C) Histogram overlays (B) and bar graphs (C) showing the fluorescence intensity of BCL-6 staining in GC and non-GC B cells as gated in A derived from the CD45.1 Il21r+/+ or CD45.2 Il21−/− compartment of CD45.1 Il21r+/+/CD45.2 Il21r−/− mixed bone marrow chimeras 6 d after SRBC immunization. The horizontal dashed line highlights the median levels of Bcl-6 found in non-GC B cells. Each set of two bars represents the data from the CD45.1 and CD45.2 compartments of a single mouse. MFI, mean fluorescence intensity.
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fig5: Lack of IL-21R signaling reduces the expression of Bcl-6 in GC B cells. (A) Flow cytometric contour plots indicating the gating strategy for non-GC and GC B220+ cells (left) and BCL-6 expression on GL-7+ (middle) and Fas+ (right) B cells. (B and C) Histogram overlays (B) and bar graphs (C) showing the fluorescence intensity of BCL-6 staining in GC and non-GC B cells as gated in A derived from the CD45.1 Il21r+/+ or CD45.2 Il21−/− compartment of CD45.1 Il21r+/+/CD45.2 Il21r−/− mixed bone marrow chimeras 6 d after SRBC immunization. The horizontal dashed line highlights the median levels of Bcl-6 found in non-GC B cells. Each set of two bars represents the data from the CD45.1 and CD45.2 compartments of a single mouse. MFI, mean fluorescence intensity.

Mentions: To test this hypothesis, we quantified Bcl-6 protein levels by flow cytometry in mixed CD45.1 Il21r+/+/CD45.2 Il21r−/− chimeric mice 6 d after SRBC immunization. As expected, Bcl-6 was up-regulated in GC B cells compared with non-GC B cells (Fig. 5, A and B). Strikingly, in every mouse analyzed, GC B cells lacking IL-21R expression showed a significant reduction (P = 0.002) in Bcl-6 levels compared with Il21r+/+ GC B cells in the same mouse (Fig. 5, B and C). This suggests that IL-21 contributes to GC B cell formation by signaling directly in B cells to induce maximal expression of Bcl-6. There are multiple ways by which Bcl-6 defects may impair affinity maturation: by decreasing the efficiency of somatic hypermutation through direct or indirect effects on AID expression; by promoting early differentiation and exit of GC B cells from the GCs, preventing them from undergoing successive rounds of mutation; or by reducing the ability of GC B cells to interact and elicit survival signals from follicular DCs or Tfh cells.


IL-21 acts directly on B cells to regulate Bcl-6 expression and germinal center responses.

Linterman MA, Beaton L, Yu D, Ramiscal RR, Srivastava M, Hogan JJ, Verma NK, Smyth MJ, Rigby RJ, Vinuesa CG - J. Exp. Med. (2010)

Lack of IL-21R signaling reduces the expression of Bcl-6 in GC B cells. (A) Flow cytometric contour plots indicating the gating strategy for non-GC and GC B220+ cells (left) and BCL-6 expression on GL-7+ (middle) and Fas+ (right) B cells. (B and C) Histogram overlays (B) and bar graphs (C) showing the fluorescence intensity of BCL-6 staining in GC and non-GC B cells as gated in A derived from the CD45.1 Il21r+/+ or CD45.2 Il21−/− compartment of CD45.1 Il21r+/+/CD45.2 Il21r−/− mixed bone marrow chimeras 6 d after SRBC immunization. The horizontal dashed line highlights the median levels of Bcl-6 found in non-GC B cells. Each set of two bars represents the data from the CD45.1 and CD45.2 compartments of a single mouse. MFI, mean fluorescence intensity.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2822609&req=5

fig5: Lack of IL-21R signaling reduces the expression of Bcl-6 in GC B cells. (A) Flow cytometric contour plots indicating the gating strategy for non-GC and GC B220+ cells (left) and BCL-6 expression on GL-7+ (middle) and Fas+ (right) B cells. (B and C) Histogram overlays (B) and bar graphs (C) showing the fluorescence intensity of BCL-6 staining in GC and non-GC B cells as gated in A derived from the CD45.1 Il21r+/+ or CD45.2 Il21−/− compartment of CD45.1 Il21r+/+/CD45.2 Il21r−/− mixed bone marrow chimeras 6 d after SRBC immunization. The horizontal dashed line highlights the median levels of Bcl-6 found in non-GC B cells. Each set of two bars represents the data from the CD45.1 and CD45.2 compartments of a single mouse. MFI, mean fluorescence intensity.
Mentions: To test this hypothesis, we quantified Bcl-6 protein levels by flow cytometry in mixed CD45.1 Il21r+/+/CD45.2 Il21r−/− chimeric mice 6 d after SRBC immunization. As expected, Bcl-6 was up-regulated in GC B cells compared with non-GC B cells (Fig. 5, A and B). Strikingly, in every mouse analyzed, GC B cells lacking IL-21R expression showed a significant reduction (P = 0.002) in Bcl-6 levels compared with Il21r+/+ GC B cells in the same mouse (Fig. 5, B and C). This suggests that IL-21 contributes to GC B cell formation by signaling directly in B cells to induce maximal expression of Bcl-6. There are multiple ways by which Bcl-6 defects may impair affinity maturation: by decreasing the efficiency of somatic hypermutation through direct or indirect effects on AID expression; by promoting early differentiation and exit of GC B cells from the GCs, preventing them from undergoing successive rounds of mutation; or by reducing the ability of GC B cells to interact and elicit survival signals from follicular DCs or Tfh cells.

Bottom Line: To date, it is unclear whether the effect of IL-21 on GC formation is predominantly a consequence of this cytokine acting directly on the Tfh cells or if IL-21 directly influences GC B cells.IL-21 deficiency profoundly impaired affinity maturation and reduced the proportion of IgG1(+) GC B cells but did not affect formation of early memory B cells.In contrast to the requirement for IL-21 in the follicular response to sheep red blood cells, a purely extrafollicular antibody response to Salmonella dominated by IgG2a was intact in the absence of IL-21.

View Article: PubMed Central - HTML - PubMed

Affiliation: John Curtin School of Medical Research, Australian National University, Canberra, ACT 2601, Australia.

ABSTRACT
During T cell-dependent responses, B cells can either differentiate extrafollicularly into short-lived plasma cells or enter follicles to form germinal centers (GCs). Interactions with T follicular helper (Tfh) cells are required for GC formation and for selection of somatically mutated GC B cells. Interleukin (IL)-21 has been reported to play a role in Tfh cell formation and in B cell growth, survival, and isotype switching. To date, it is unclear whether the effect of IL-21 on GC formation is predominantly a consequence of this cytokine acting directly on the Tfh cells or if IL-21 directly influences GC B cells. We show that IL-21 acts in a B cell-intrinsic fashion to control GC B cell formation. Mixed bone marrow chimeras identified a significant B cell-autonomous effect of IL-21 receptor (R) signaling throughout all stages of the GC response. IL-21 deficiency profoundly impaired affinity maturation and reduced the proportion of IgG1(+) GC B cells but did not affect formation of early memory B cells. IL-21R was required on GC B cells for maximal expression of Bcl-6. In contrast to the requirement for IL-21 in the follicular response to sheep red blood cells, a purely extrafollicular antibody response to Salmonella dominated by IgG2a was intact in the absence of IL-21.

Show MeSH
Related in: MedlinePlus