We will take advantage of a unique observation from our laboratory, based on our work in primary biliary cirrhosis (PBC), considered a model autoimmune disease, that plasmablasts (PB) play a critical role in ongoing immune activation and loss of tolerance. We have demonstrated the striking finding that in PBC, on average, 10% of the total IgG and IgA and 23% of the IgM PB population, are specific for the immunodominant mitochondrial autoantigen, PDC-E2, the signature autoantigen in this disease. Further, our data reflect that PB-derived autoantibodies recognize only native PDC-E2, whereas serum from the same patient recognize native PDC-E2 and xenobiotic modified PDC-E2. These data take on additional significance based on work suggesting that PBC is induced following exposure to environmental chemicals that facilitate loss of tolerance in genetically susceptible hosts. Sera autoantibodies reflect long-term resident plasma cells, whereas the PB reactivity reflects current and ongoing B cell responses. Our data suggests that a better understanding of PB is key to dissecting the loss of immune tolerance that leads to biliary autoimmunity and we postulate that there are two categories of PB that are critical in the inflammatory liver microenvironment, including 1) PB arising from memory B cells, previously primed by xenobiotics, subsequently undergoing somatic hypermutation to obtain higher affinity for PDC-E2 while losing their binding activity for the priming xenobiotics, and 2) PB derived from naive B cells directly activated by PDC-E2 autoantigen and memory B cells originally primed by PDC-E2. We will address this proposal using two specific aims. Firstly, we will elucidate in detail the ongoing PDC-E2 specific PB response through global characterization of the autoantigen-specific PB cell repertoire, including isotype distribution and lineage structure of the B cell clones in each isotype. This wil allow us to identify PDC-E2-specific clones of each Ig isotype and provides an overall picture for the ongoing autoreactive PB response in PBC. We expect to identify evolutionally related IgG and IgA clones to those in the IgM population, which are likely derived from naive or re-activated memory B cells primed by PDC-E2 autoantigen, as well as the independent clones that are derived from memory B cells potentially primed by xenobiotics. Second, to verify that PDC-E2 specific PB reactivities arose originally from xenobiotic reactive antibodies, we will revert highl mutated PDC-E2-specific IgG or IgA sequences back to their germline sequences. Functionally relevant binding activities to native PDC-E2 and xenobiotics will be compared between PB-derived mAb and germline reverted Ig clones. These data will provide evidence for the environmental etiology of PBC and allow us to produce recombinant mAbs against PDC-E2 and germline reverted engineered antibodies, powerful tools for a functional approach to address the pathogenic functions of AMAs and xenobiotic-reactive antibodies. Finally, our approach of reverting hypermutated antibody to germline sequences provides a unique molecular approach to defining the role of B cells in loss of tolerance.

Public Health Relevance

Our laboratory has been studying the etiology of an autoimmune disease predominantly of women, called primary biliary cirrhosis. This disease leads to destruction of small bile ducts in the liver of affected patients. In this proposal we propose to take advantage of some recent data from our laboratory that revolves around the proposed environmental etiology of this disease. In particular, we have found that a special type of white cell, called a plasmablast, secretes a different group of antibodies than those traditionally measured in sera. We propose to take advantage of this observation to help identify the earliest population of autoantibodies produced and how that influences subsequent disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21AI115120-02
Application #
8974256
Study Section
Transplantation, Tolerance, and Tumor Immunology (TTT)
Program Officer
Johnson, David R
Project Start
2014-12-01
Project End
2017-11-30
Budget Start
2015-12-01
Budget End
2017-11-30
Support Year
2
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of California Davis
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
047120084
City
Davis
State
CA
Country
United States
Zip Code
95618
Song, Junmin; Lleo, Ana; Yang, Guo Xiang et al. (2018) Common Variable Immunodeficiency and Liver Involvement. Clin Rev Allergy Immunol 55:340-351
Tanaka, Toshihiro; Zhang, Weici; Sun, Ying et al. (2017) Autoreactive monoclonal antibodies from patients with primary biliary cholangitis recognize environmental xenobiotics. Hepatology 66:885-895