NEWS
   
 

Prof. Wanli Liu and Zhanguo Li published a Science paper reporting a novel mechanism on the regulation and activation of B lymphocytes in autoimmune diseases

 

Two teams led by Wanli Liu from the School of Life Sciences at Tsinghua University, and by Zhan-Guo Liu from the Department of Rheumatology and Immunology of Peking University People's Hospital, published a paper in Science entitled "Autoimmune disease variant of IgG1 modulates B Cell activation and differentiation’’. The single-nucleotide polymorphism (SNP), which is positively correlated with systemic lupus erythematosus (SLE), was first reported in human membrane-bound immunoglobulin IgG1 heavy chain intracellular domain, and revealed that this SNP is involved in the regulation of B cell fate determination. The novel finding provides potential drug targets and theoretical support for the study of pathogenic mechanisms and preventive treatment of autoimmune diseases.

Autoimmune diseases such as systemic lupus erythematosus (SLE) are characterized by the presence of large numbers of self-reactive antibodies that induce deposition of immune complexes (ICs) leading to inflammation and tissue damage. Auto-reactivity is pervasive in the antibody repertoire of human B cells across different developmental stages. It is especially enriched in the peripheral IgG+ memory B-cell pool, but is efficiently diminished in the plasma-cell compartment in healthy individuals. However, these checkpoints fail in patients with autoimmune diseases. It remains unclear how autoreactive IgG+ B cells are maintained in a quiescent state under physiological immune homeostasis, and how these checkpoints are broken in pathological conditions.

Wanli Liu’s team proposed a hypothesis that the abnormal activation of IgG-type B cell receptor (IgG-BCR) may be involved in the pathogenesis of autoimmune diseases. Collaborating with three clinical hospitals in Beijing and Shenzhen led by Dr. Zhan-Guo Li, they identified a single-nucleotide polymorphism (SNP) rs117518546, which results in a glycine-to-arginine substitution at codon 396 in human IgG1 (hIgG1-G396R). This SNP was common in East Asian populations, and was significantly correlated with susceptibility to SLE. The G396R variant frequency was substantially enriched in SLE patients compared to criteria-matched controls in three independent cohorts from multi-clinical centers in China (1,786 healthy controls vs 1,838 SLE patients in total, P=6.0E-5). Furthermore, the G396R variant was associated with a more severe disease phenotype, including earlier onset, multiple organ involvement, and higher SLE disease activity, specifically aggravated autoantibody production, and inflammation. The variant drove an autoantibody subclass profile shift towards IgG1 isotype predominance in G396R patients. Thus, hIgG1-G396R is a risk locus for SLE.

Liu Wanli team generated knock-in mice harboring the murine homologue mIgG1-G390R. In the autoimmune induction model, mice carrying the SNP produced more extensive autoantibodies, which depended on the large number of B cells stimulated by the antigen themselves. The differentiation of autoreactive plasma cells confirms the findings in patients with SLE and gives a preliminary explanation from the B cell fate determination level. At the same time, in view of the high frequency of SNPs in East Asians and the important role of IgG-type memory B cell production and function in vaccine immunization, the Liu Wanli team explored the impact of SNP on antibody response stimulated by normal vaccination. A cohort study of healthy volunteers immunized with seasonal influenza vaccine revealed that the homozygous carrier of this SNP had a significantly higher influenza virus-specific IgG1 antibody response than healthy volunteers who did not carry the SNP. This result indicates that the SNP has a typical "double-edged sword" effect on the regulation of IgG-type B cell-mediated antibody responses: on the one hand, it promotes the production of protective antibodies, and helps to resist pathogen invasion; on the other hand, in the case of immune abnormalities, the memory B cells with self-reactivity exacerbate the production of autoantibodies and promote the occurrence and deterioration of SLE.

Liu Wanli team has integrated high-speed high-resolution living cell single-molecule imaging platform based on total internal reflection fluorescence microscope (TIRF) and Matlab-based single-molecule trajectory tracking algorithm, to reveal that this SNP significantly prolongs the residence time of the downstream signaling molecule Grb2 in B cell immune synapses after IgG-BCR activation. Further molecular dynamics simulation revealed that the SNP variation interacts with Lyn kinase by forming new kinase-substrate amino acid residues (kinase 290 asparagine and substrate 390 arginine). The formation of hydrogen bonds significantly enhances the binding of the Lyn kinase domain to the ITT motif, which in turn greatly promotes the phosphorylation efficiency of Lyn on the ITT motif. The density of phosphorylated ITT is significantly increased, thereby changing the recruitment pattern of Grb2 in the immune synapse, from Recruit and Escape to Recruit and Confine. The residence time is more effective in promoting the formation of Grb2-BTK-PLCγ2 signaling bodies in immune synapses, greatly enhancing the immune activation of downstream signaling pathways including NF-κB, Erk, up-regulating transcription factors Blimp1 and Irf4 which determines the fate of B cell-activated plasma cells to differentiate into antibody-secreting plasma cells.

Dr. Xiangjun Chen, who graduated from the School of Life Sciences in January 2018, is the first author of the thesis. Prof. Liu Wanli, from the School of Life Sciences and Institute for Immunology is the corresponding author of the paper. Prof. Li Zhanguo, from the Department of Rheumatology and Immunology of Peking University People's Hospital is the co-corresponding author. The research was supported by the Experimental Animal Center and Biomedical Testing Center of Tsinghua University. The research was funded by the National Natural Science Foundation of China, the Ministry of Science and Technology, the Youth Thousand Talents Program, the Institute of Immunology of Tsinghua University, and Center for Life Sciences.

Liu Wanli lab has been committed to the application of novel high-speed and high-resolution living cell single-molecule fluorescence imaging technology, combined with traditional molecular immunology, biochemistry and biophysics research methods, B lymphocyte immune recognition, immune activation and research on the pathogenesis of related immune diseases. Liu Wanli has published lots of papers as correspondence authors (including Common): Cell, Leukemia, Science Immunology, J Exp Med, PNAS, eLife (2015 and 2017), J Cell Biol, Nature Communications (2015 and 2017), Science Signaling, Cell Research (2014 and 2018), Cell Reports, J Immunol (2013, 2014 and 2017), Eur J Immunol, Frontiers in Immunology, Trends ln Immunology.

The team of Li Zhanguo has long been engaged in the pathogenesis and immunotherapy of autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. He has obtained a number of clinical diagnosis and immunotherapy achievements under the support of the National Key Clinical Specialties of Rheumatology and the 973 Program. He has more than 200 SCI papers that have been published in the journals of Nature Medicine (2016), Cell Host Microbe (2016), Immunity (2013), J Exp Med, Ann Rheum Dis (2016, 2015, 2015, 2014, 2011). Links to the publication: http://science.sciencemag.org/content/362/6415/700.long