The lipid globotriaosylceramide promotes germinal center B cell responses and antiviral immunity

• 成果类型: Article
• 署名作者: Sharma, Pankaj; Zhang, Xiaolong; Ly, Kevin; Zhang, Yuxiang; Hu, Yu; Ye, Adam Yongxin; Hu, Jianqiao; Kim, Ji Hyung; Lou, Mumeng; Wang, Chong; Celuzza, Quinton; Kondo, Yuji; Furukawa, Keiko; Bundle, David R.; Furukawa, Koichi; Alt, Frederick W.; Winau, Florian
• 署名单位: Harvard University; Harvard University Medical Affiliates; Boston Children's Hospital; Program in Cellular & Molecular Medicine (PCMM); Harvard Medical School; Harvard University; Harvard University Medical Affiliates; Boston Children's Hospital; Program in Cellular & Molecular Medicine (PCMM); Howard Hughes Medical Institute; Harvard Medical School; Nagoya University; Chubu University; University of Alberta; Korea University; Harvard University; Massachusetts Institute of Technology (MIT); Broad Institute
• 刊物名称: SCIENCE
• ISSN/ISSBN: 0036-9214
• DOI: 10.1126/science.adg0564
• 发表日期: 2024-02-16
• 关键词: transcription factor; somatic mutation; coreceptor cd19; pi3 kinase; receptor; antibodies; selection; binding; region; proliferation

摘要

INTRODUCTION Viral infections, such as influenza, impose a substantial burden on public health. In the absence of potent antiviral drugs, vaccination is the best strategy to control infectious disease. The goal of efficient vaccines is the induction of an immune response that is characterized by production of antibodies of high affinity and broad reactivity. The diversity of antibodies is especially important to facilitate cross-protective immunity in response to mutating viral strains. Antibody-producing B lymphocytes are central players in humoral immunity. After initial activation, B cells are recruited to anatomical structures called germinal centers (GCs), in which B cells mutate their antibody sequences to increase their affinity for antigen and processes of B cell selection occur that promote the diversity of the antibody repertoire. RATIONALE Globotriaosylceramide (Gb3) is a glycosphingolipid abundantly expressed on GC B cells. Although used as a marker for these cells, it was not known whether Gb3 could regulate the function of B cells. We used genetically modified mouse models to deplete or increase the abundance of Gb3 in GC B cells to investigate its function in regulating humoral immune responses. In the dark zone of the GC, B cells undergo affinity maturation on the basis of a process called somatic hypermutation, by introducing mutations into antibody sequences to augment their affinity. B cell receptor (BCR) signaling triggers a downstream cascade that is required for migration of GC B cells out of the dark zone. Subsequently, B cells arrive in the light zone of the GC, where they perform antigen presentation through major histocompatibility complex class II (MHC-II) to T follicular helper (TFH) cells driving B cell selection and diversity. We therefore investigated somatic hypermutation, BCR signaling, GC B cell cycling, and MHC-II presentation to understand the impact of the lipid Gb3 on antibody affinity and diversity. RESULTS We found that Gb3 specifically binds to the plasma membrane glycoprotein CD19, disrupting the interaction with its chaperone CD81 and allowing CD19 to recruit and activate kinases associated with BCR signaling. This signaling pathway, which was dependent on the presence of Gb3, triggered the degradation of the transcription factor FOXO1. Reduction in FOXO1 caused gene expression changes that allowed GC B cells to transition from the dark zone, where somatic hypermutation happens, to the light zone, where B cell selection occurs. Thus, the Gb3-dependent CD19 translocation mechanism facilitated BCR signaling and GC B cell dynamics that overall promoted affinity maturation of B cells. Conversely, in the absence of Gb3, CD19 remained in complex with CD81 and failed to translocate to the BCR, consequently abrogating downstream signaling, FOXO1 degradation, and GC B cell cycling. As a result, without Gb3, B cells were not able to undergo affinity maturation and failed to produce high-affinity antibodies. Furthermore, the lipid Gb3 supported the surface expression of MHC-II levels on GC B cells, which facilitated the activation of T-FH cells. Through this mechanism, Gb3 could promote selection of B cell clones reactive with subdominant epitopes, which are antigens that remain unrecognized in a conventional immune response, indicating that Gb3 amplifies antibody diversity. We observed that, when used as an adjuvant in vaccination against influenza virus in mice, Gb3 triggered antibody responses reactive with the stalk of viral hemagglutinin, which, in contrast to its globular head, harbors conserved antigenic determinants. This broader Gb3-mediated B cell response proved to be cross-protective against other strains of influenza. CONCLUSION Our work introduces the lipid Gb3 as a protagonist in the GC response, determining affinity as well as diversity of antibodies. From these findings, we propose that Gb3 has the potential to act as an adjuvant for vaccination against viral infections. Gb3 drives affinity and diversity of antibody responses and protects against viral infection. In GC B cells, Gb3 binds to CD19 and disengages it from its chaperone CD81 for subsequent translocation to the BCR to mediate downstream signaling and affinity maturation. Moreover, Gb3 regulates MHC-II levels to facilitate selection of TFH cells and GC B cells of increased diversity. In vaccination with recombinant hemagglutinin (rHA), the use of Gb3 as an adjuvant triggers broadly neutralizing antibodies and broad protection against influenza. FDC, follicular dendritic cell; TCR, T cell receptor. [Created with BioRender.com]