Through an ITIM-independent mechanism the FcγRIIB blocks B cell activation by disrupting the colocalized microclustering of the B cell receptor and CD19.
B cell activation is regulated through the interplay of the BCR with the inhibitory coreceptor FcγRIIB and the activating coreceptor CD19. Recent studies suggest that Ag-driven BCR microclusters are efficiently converted to a signaling active state on colocalization with CD19 microclusters. Using total internal reflection fluorescence microscopy-based, high-resolution, high-speed live-cell and molecule imaging approaches, we show that when co-ligated to the BCR, the FcγRIIB can inhibit B cell activation by blocking the colocalization of BCR and CD19 microclusters within the B cell immunological synapse. Remarkably, this inhibitory function of FcγRIIB is dependent not on its well-characterized ITIM-containing cytoplasmic domain, but its transmembrane domain. Indeed, human primary B cells from systemic lupus erythematosus patients homozygous for gene encoding the loss-of-function transmembrane domain mutant FcγRIIB-I232T fail to block the synaptic colocalization of the BCR with CD19, leading to dysregulated recruitment of downstream signaling molecule p-PI3K to membrane proximal signalosome. This inhibitory function of FcγRIIB in impairing the spatial-temporal colocalization of BCR and CD19 microclusters in the B cell immunological synapse may help explain the hyper-reactive features of systemic lupus erythematosus patient B cells in reported studies. These observations may also provide new targets for therapies for systemic autoimmune disease.
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China; Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100730, China;
Liling
L
Xu
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China; Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100730, China;
Gen
G
Li
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China;
Jing
J
Wang
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China;
Yilin
Y
Fan
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China;
Zhengpeng
Z
Wan
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China;
Shaosen
S
Zhang
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China;
Samina
S
Shaheen
Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100730, China; Key Laboratory of Rheumatology and Clinical Immunology, Ministry of Education, Beijing, 100730, China;
Jing
J
Li
Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100730, China; Key Laboratory of Rheumatology and Clinical Immunology, Ministry of Education, Beijing, 100730, China;
Li
L
Wang
Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100730, China; Key Laboratory of Rheumatology and Clinical Immunology, Ministry of Education, Beijing, 100730, China;
Cai
C
Yue
Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100730, China; Key Laboratory of Rheumatology and Clinical Immunology, Ministry of Education, Beijing, 100730, China;
Yan
Y
Zhao
Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China;
Fei
F
Wang
Laboratory of Immunogenetics Imaging Facility, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852; and.
Joseph
J
Brzostowski
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China; liuwanli@biomed.tsinghua.edu.cn wenjzheng@gmail.com chenyh@mail.tsinghua.edu.cn.
Ying-Hua
YH
Chen
Department of Rheumatology and Clinical Immunology, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, 100730, China; Key Laboratory of Rheumatology and Clinical Immunology, Ministry of Education, Beijing, 100730, China; liuwanli@biomed.tsinghua.edu.cn wenjzheng@gmail.com chenyh@mail.tsinghua.edu.cn.
Wenjie
W
Zheng
Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, 100084, China; Collaborative Innovation Center for Infectious Diseases, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, 310003, China liuwanli@biomed.tsinghua.edu.cn wenjzheng@gmail.com chenyh@mail.tsinghua.edu.cn.
Wanli
W
Liu
D019943:Amino Acid Substitution; D000818:Animals; D018941:Antigens, CD19 / Q000235:genetics / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology* / Q000473:pathology; D006801:Humans; D054992:Immunological Synapses / Q000235:genetics / Q000276:immunology / Q000473:pathology; D008180:Lupus Erythematosus, Systemic / Q000235:genetics / Q000276:immunology* / Q000473:pathology; D008213:Lymphocyte Activation; D051379:Mice; D020125:Mutation, Missense; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000276:immunology; D017434:Protein Structure, Tertiary; D011947:Receptors, Antigen, B-Cell / Q000235:genetics / Q000276:immunology*; D017452:Receptors, IgG / Q000235:genetics / Q000276:immunology*
D018941:Antigens, CD19; C499173:FCGR2B protein, human; C499172:Fcgr2b protein, mouse; D011947:Receptors, Antigen, B-Cell; D017452:Receptors, IgG; D019869:Phosphatidylinositol 3-Kinases