Journal of Immunology Research

Journal of Immunology Research / 2020 / Article

Research Article | Open Access

Volume 2020 |Article ID 1859260 | https://doi.org/10.1155/2020/1859260

Chuan Wei, Ying Chen, Lei Xu, Beibei Yu, Di Lu, Yanxiong Yu, Zhigang Lei, Rui Tang, Sha Zhou, Jifeng Zhu, Xiaojun Chen, Chuan Su, "CD40 Signaling Promotes CXCR5 Expression in B Cells via Noncanonical NF-κB Pathway Activation", Journal of Immunology Research, vol. 2020, Article ID 1859260, 6 pages, 2020. https://doi.org/10.1155/2020/1859260

CD40 Signaling Promotes CXCR5 Expression in B Cells via Noncanonical NF-κB Pathway Activation

Academic Editor: Nejat K. Egilmez
Received09 Jun 2020
Accepted16 Jul 2020
Published31 Jul 2020

Abstract

Chemokine receptor CXCR5-mediated control of B cell trafficking in the lymphoid tissues plays a central role in orchestrating the B cell function, which not only guides the colocalization of B cells with follicular helper T cells in the follicular mantle zone but also determines the position of germinal center dark and light zones. However, the mechanisms that regulate the expression of CXCR5 in B cells remain unclear. Here, we show that the expression level of CXCR5 in B cells was substantially reduced in vitro culture conditions, while being maintained in the presence of CD40 signals. Furthermore, CD40 signaling promotes CXCR5 expression in B cells at least partially through noncanonical NF-κB signaling pathway activation. However, other non-B cells also contributed to the optimal expression of CXCR5 in B cells through cell-cell contact and cytokine secretion. Our findings suggest that CD40 signaling-mediated activation of the noncanonical NF-κB pathway promotes the expression of CXCR5 in a B cell-intrinsic way to orchestrate the trafficking of B cells.

1. Introduction

B cells are key players of the adaptive humoral immune, with roles including supporting follicular helper T-cell generation and producing antibodies [1, 2]. The outcome of these functions relies on the finely tuned traffic of B cells [3]. CXC chemokine receptor 5-mediated signals play a central role in orchestrating B cell trafficking in the lymphoid tissues, such as spleen and lymph nodes [4]. Indeed, CXCR5 signaling directly guides the colocalization of B cells with CXCR5+ T cells in the follicular mantle zone to support the generation of follicular helper T cells [5]. In addition, CXCR5 signaling directs B cells to the light zone and determines the position of germinal center dark and light zones, which segregate cells undergoing somatic hypermutation and antigen-driven selection to guide the germinal center reaction [6, 7]. Although CXCR5-mediated control of B cell trafficking plays a cardinal role in orchestrating the B cell functions, little is known about the underlying mechanisms that regulate the expression of CXCR5 in B cells.

CD40-mediated signals in B cells are particularly important for germinal center formation and humoral immune responses by orchestrating B cell functions [8]. Indeed, CD40 signaling plays multiple roles in B cell activation, proliferation, class-switch recombination, and affinity maturation [9]. The germinal center reaction is severally impaired in the absence of CD40-mediated signals and individuals with defective CD40-mediated signals are suffering from hyper-IgM syndrome with reduced germinal centers and class-switched B cells [10], which support the importance of CD40 signals in the generation of germinal center and high-affinity antibody responses. Given that CD40 is essential for CXCR5 expression in MDSCs [11], we wonder whether CD40 signaling is also involved in the regulation of CXCR5 expression in B cells.

In this study, we found a remarkably reduced expression of CXCR5 in B cells in vitro culture conditions, while being maintained in the presence of CD40 signal. Indeed, CD40 signaling promotes the expression of CXCR5 in a B cell-intrinsic way in part via noncanonical NF-κB pathway activation. In addition, our results showed that other non-B-cell splenocytes were also involved in the optimal expression of CXCR5 in B cells through cell-cell contact and cytokine secretion. Our findings suggest that CD40-mediated expression of CXCR5 may contribute to the regulation of B cell trafficking.

2. Materials and Methods

2.1. Mice

Male wild-type C57BL/6 mice were obtained from the Animal Core Facility of Nanjing Medical University (Nanjing, China) and housed under specific pathogen-free conditions in accredited animal facilities at Nanjing Medical University. All procedures were conducted in accordance with the Regulations for the Administration of Affairs Concerning Experimental Animals (1988.11.1). All animal procedures were approved by the Institutional Animal Care and Use Committee (IACUC) of Nanjing Medical University for the use of laboratory animals (Permit Number: IACUC-1701019).

2.2. Flow Cytometry

Cells were isolated from spleens using mechanical disruption followed by red blood cell (RBC) lysis. Fc receptors of cells were blocked with anti-mouse CD16/CD32 (eBioscience, San Diego, CA) for 15 minutes at 4°C prior to antibody staining. Then, cells were incubated for 30 min at 4°C with the following antibodies: CD19-FITC (eBioscience), CXCR5-APC (BD Biosciences, San Jose, CA), and CD40-PE (eBioscience). After washing twice with PBS containing 1% FBS, cells were characterized using a FACSVerse cytometer (BD Biosciences). Data were analysed with FlowJo (Tree Star, version 10.0.7).

2.3. In Vitro Cell Coculture and Stimulation

B cells were purified from splenocytes using anti-B220 conjugated magnetic beads (Miltenyi Biotec GmbH, Bergisch Gladhach, Germany). Unless specifically noted otherwise, the purified B cells or splenocytes were stimulated in vitro by agonistic anti-mouse CD40 antibody (500 ng/mL; BioLegend, San Diego, CA), Recombinant BAFF (200 ng/mL; Thermo Fisher Scientific, Waltham, MA), or NIK inhibitor (10 ug/mL; MedChemExpress, Shanghai, China) for 72 hours. In parallel cultures, B cells were separated from non-B cell splenocytes by a porous (0.4 mm) membrane in otherwise identical conditions.

2.4. Western Blots

Splenocytes treated with anti-CD40 in the presence or absence of NIK inhibitor for 72 hours were homogenized in lysis buffer (Cell Signaling Technology, Danvers, MA) with 1 mM PMSF (Beyotime Biotech, Nantong, China). The protein concentration was determined using a bicinchoninic acid (BCA) Protein Assay kit (Thermo Fisher Scientific). Immunoblotting was performed using the following antibodies: anti-GAPDH (Abcam, Cambridge, MA), anti-p100/p52 (Cell Signaling Technology), and anti-RelB (Santa Cruz Biotechnology, Santa Cruz, CA).

2.5. Statistical Analysis

Statistics and graphing were conducted in GraphPad Prism 5.0 software. Error bars indicate s.d. Data were analyzed by two-tailed unpaired Student’s -test for two-group comparison and ANOVA test for three or more-group comparison. value of less than 0.05 was considered significant.

3. Results and Discussion

3.1. CXCR5 Was Gradually Reduced in B Cells In Vitro Culture Conditions

To study the underlying mechanisms that regulate the expression of CXCR5 in B cells, splenocytes were isolated from normal mice and cultured in vitro. The levels of CXCR5 in B cells were detected with flow cytometer by staining CD19 and CXCR5 (Figure 1(a)) and displayed a dramatic reduction in a time-dependent manner, while freshly isolated B cells displayed constitutive CXCR5 expression, reflected by mean fluorescence intensity (MFI) of CXCR5 (Figures 1(b) and 1(c)) and frequencies of CXCR5+ cells (Figure 1(d)) in B cells, suggesting that the microenvironmental cues in vivo were necessary for maintaining CXCR5 expression in B cells.

3.2. CD40 Signaling Promoted CXCR5 Expression in a B Cell-Intrinsic Way

Given that B cells are constantly exposed to BAFF stimulation in vivo [12], we first wondered whether BAFF had an ability to maintain CXCR5 expression in B cells. The results showed that the expressions of CXCR5 in B cells in the presence of BAFF were maintained slightly better than those in the absence of BAFF (Supporting Information Figure 1). These results suggested that BAFF may be not a major contributor to maintain the high expression levels of CXCR5 in B cells. The other factors for maintaining CXCR5 in B cells needed to be further investigated.

Since CD40 signaling has multiple roles in orchestrating B cell functions, we wondered whether CD40 signaling might contribute to the induction of CXCR5 expression in B cells. To test this hypothesis, we analyzed the expressions of CD40 and CXCR5 in B cells and found a coexpression of CD40 and CXCR5 (Figure 2(a)), suggesting that CD40 signaling might be involved in the regulation of CXCR5 expression in B cells. Moreover, we cultured splenocytes in the presence of CD40 signals and found that CD40 signaling promoted CXCR5 expression in B cells in vitro, reflected by frequencies of CXCR5+ cells (Supporting Information Figures 2(a) and 2(b)) and MFI of CXCR5 (Supporting Information Figures 2(c) and 2(d)) in B cells. To evaluate whether CD40 signaling directly affected the expression of CXCR5 in B cells, B cells were sorted by the magnetic cell sorting. The purity of sorted B cells was determined to be greater than 99% (Figure 2(b)). Of note, CD40 signaling promoted the expression of CXCR5 by directly targeting B cells (Figures 2(c) and 2(d)). Given that CD40L is primarily expressed on antigen-stimulated CD4+ T cells [13], we reasoned that CD40 signaling might be involved in the regulation of B cell traffic during an immune response through promoting CXCR5 expression in B cells. In addition, other non-B cells also contributed to the optimal expression of CXCR5 in B cells through cell-cell contact and cytokine secretion (Figures 2(c) and 2(d)). Taken together, these results demonstrated that CD40 signaling promoted CXCR5 expression in a B cell-intrinsic manner, while non-B cells also contributed to the optimal expression of CXCR5 in B cells.

3.3. CD40-Mediated Activation of Noncanonical NF-κB Signalling Contributed to CXCR5 Expression in B Cells

Given that CD40 signaling in B cells induced the activation of the noncanonical NF-κB pathway, we wondered whether noncanonical NF-κB signalling was involved in CD40-mediated induction of CXCR5 expression in B cells. Notably, the expressions of RelB and P52, key regulators of the noncanonical NF-κB pathway, were strongly increased in B cells treated with anti-CD40 agonistic antibody (Figure 3(a)). While inhibition of NF-κB-inducing kinase (NIK), a central component of the noncanonical NF-κB pathway, considerably impaired CD40-mediated CXCR5 expression in B cells, reflected by decreases in the percentages of CXCR5+ B cells (Figures 3(b) and 3(c)) and the MFI of CXCR5 in B cells (Figures 3(d) and 3(e)), which was associated with reduced levels of RelB and P52 (Figure 3(a)). In conclusion, our data indicated that CD40 signaling promoted the expression of CXCR5 in B cells at least partially through noncanonical NF-κB pathway activation.

4. Conclusions

CXCR5-mediated signals have a pivotal role in regulating B cell trafficking, which is important for orchestrating the functions of B cells including supporting follicular helper T-cell generation and producing antibodies. We showed that CD40 signaling promoted the expression of CXCR5 in a B cell-intrinsic manner in part through noncanonical NF-κB pathway activation, while other non-B cells were involved in the optimal expression of CXCR5 in B cells. Our findings suggest that CD40-mediated induction of CXCR5 expression may contribute to orchestrating B cell function through controlling B cell trafficking.

Data Availability

All data are fully available without restriction.

Conflicts of Interest

The authors declare no commercial or financial conflict of interest.

Authors’ Contributions

Chuan Wei, Ying Chen, and Lei Xu contributed equally to this work.

Acknowledgments

This work was supported by the grants from the grant of the National Key Research and Development Program of China (MOST No: 2018YFA0507300) and the National Natural Science Foundation of China (No: 81871675, No: 81430052) and to Chuan Su, and the grants from the National Natural Science Foundation of China (No: 81871676) and Natural Science Foundation of Jiangsu Province (No: BK20190082) to Xiaojun Chen. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Supplementary Materials

Supporting Information Figure 1: BAFF promotes CXCR5 expression in B cells. Supporting Information Figure 2: CD40 signal promotes CXCR5 expression in B cells. (Supplementary Materials)

References

  1. M. D. Cooper, “The early history of B cells,” Nature Reviews Immunology, vol. 15, no. 3, pp. 191–197, 2015. View at: Publisher Site | Google Scholar
  2. M. I. Yuseff, P. Pierobon, A. Reversat, and A. M. Lennon-Dumenil, “How B cells capture, process and present antigens: a crucial role for cell polarity,” Nature Reviews Immunology, vol. 13, no. 7, pp. 475–486, 2013. View at: Publisher Site | Google Scholar
  3. F. Sallusto, C. R. Mackay, and A. Lanzavecchia, “The role of chemokine receptors in primary, effector, and memory immune responses,” Annual Review of Immunology, vol. 18, no. 1, pp. 593–620, 2000. View at: Publisher Site | Google Scholar
  4. J. G. Cyster, K. M. Ansel, V. N. Ngo, D. C. Hargreaves, and T. T. Lu, “Traffic patterns of B cells and plasma cells,” Advances in Experimental Medicine and Biology, vol. 512, pp. 35–41, 2002. View at: Publisher Site | Google Scholar
  5. P. Schaerli, K. Willimann, A. B. Lang, M. Lipp, P. Loetscher, and B. Moser, “CXC chemokine receptor 5 expression defines follicular homing T cells with B cell helper function,” The Journal of Experimental Medicine, vol. 192, no. 11, pp. 1553–1562, 2000. View at: Publisher Site | Google Scholar
  6. C. D. C. Allen, K. M. Ansel, C. Low et al., “Germinal center dark and light zone organization is mediated by CXCR4 and CXCR5,” Nature Immunology, vol. 5, no. 9, pp. 943–952, 2004. View at: Publisher Site | Google Scholar
  7. N. S. De Silva and U. Klein, “Dynamics of B cells in germinal centres,” Nature Reviews Immunology, vol. 15, no. 3, pp. 137–148, 2015. View at: Publisher Site | Google Scholar
  8. E. Gallagher, T. Enzler, A. Matsuzawa et al., “Kinase MEKK1 is required for CD40-dependent activation of the kinases Jnk and p38, germinal center formation, B cell proliferation and antibody production,” Nature Immunology, vol. 8, no. 1, pp. 57–63, 2007. View at: Publisher Site | Google Scholar
  9. R. Elgueta, M. J. Benson, V. C. de Vries, A. Wasiuk, Y. Guo, and R. J. Noelle, “Molecular mechanism and function of CD40/CD40L engagement in the immune system,” Immunological Reviews, vol. 229, no. 1, pp. 152–172, 2009. View at: Publisher Site | Google Scholar
  10. R. Allen, R. Armitage, M. Conley et al., “CD40 ligand gene defects responsible for X-linked hyper-IgM syndrome,” Science, vol. 259, no. 5097, pp. 990–993, 1993. View at: Publisher Site | Google Scholar
  11. Y. Ding, J. Shen, G. Zhang, X. Chen, J. Wu, and W. Chen, “CD40 controls CXCR5-induced recruitment of myeloid-derived suppressor cells to gastric cancer,” Oncotarget, vol. 6, no. 36, pp. 38901–38911, 2015. View at: Publisher Site | Google Scholar
  12. H. Hu, X. Wu, W. Jin, M. Chang, X. Cheng, and S. C. Sun, “Noncanonical NF-kappaB regulates inducible costimulator (ICOS) ligand expression and T follicular helper cell development,” Proceedings of the National Academy of Sciences of the United States of America, vol. 108, no. 31, pp. 12827–12832, 2011. View at: Publisher Site | Google Scholar
  13. C. van Kooten and J. Banchereau, “CD40-CD40 ligand,” Journal of Leukocyte Biology, vol. 67, no. 1, pp. 2–17, 2000. View at: Publisher Site | Google Scholar

Copyright © 2020 Chuan Wei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


More related articles

 PDF Download Citation Citation
 Download other formatsMore
 Order printed copiesOrder
Views348
Downloads317
Citations

Related articles

Article of the Year Award: Outstanding research contributions of 2020, as selected by our Chief Editors. Read the winning articles.