Autoreactive monoclonal antibodies from patients with primary biliary cholangitis recognize environmental xenobiotics

Abstract

A major problem in autoimmunity has been identification of the earliest events that lead to breach of tolerance. Although there have been major advances in dissecting effector pathways and the multi-lineage immune responses to mitochondrial self-antigens in primary biliary cholangitis (PBC), the critical links between environmental factors and tolerance remain elusive. We hypothesized that environmental xenobiotic modification of the E2 subunit of the pyruvate dehydrogenase (PDC-E2) inner lipoyl domain can lead to loss of tolerance to genetically susceptible hosts. Previously we demonstrated that serum anti-PDC-E2 autoantibodies cross-react with the chemical xenobiotics 2-octynoic acid (2-OA) and 6,8-bis (acetylthio) octanoic acid (SAc) and further that there is a high frequency of PDC-E2 specific peripheral plasmablasts. Herein we generated 104 recombinant mAbs based on paired heavy- and light-chain variable regions of individual plasmablasts derived from PBC patients. We identified 32 mAbs reactive with native PDC-E2, including 20 specific for PDC-E2 and 12 cross-reactive with both PDC-E2 and 2-OA and SAc. A lower frequency of replacement somatic hypermutations, indicating lower level of affinity maturation, was observed in the complementarity-determining regions (CDR) of the cross-reactive mAbs in comparison to mAbs exclusively recognizing PDC-E2 or those for irrelevant antigens. In particular, when the highly mutated heavy chain gene of a cross-reactive mAb was reverted to the germline sequence, the PDC-E2 reactivity was reduced dramatically whereas the xenobiotics reactivity was retained. Importantly, cross-reactive mAbs also recognized lipoic acid (LA), a mitochondrial fatty acid that is covalently bound to PDC-E2. Our data reflect that chemically modified LA or LA itself, via molecular mimicry, is the initial target that leads to the development of PBC.

Primary Biliary Cholangitis

“…Specific environmental agents that may lead to the loss of tolerance of PDC‐E2 are xenobiotics that may either mimic or modify lipoic acid, such as 2‐octynoic acid, which is common in cosmetics, and 6,8‐bis (acetylthio) octanoic acid, a metabolite of acetaminophen. AMA‐positive serum from PBC patients strongly cross‐reacts with these xenobiotics . Further experimental support for the role of xenobiotics in PBC pathogenesis comes from the ability of xenobiotics to induce a PBC‐like pathology, including AMA, in animal models …”

“…AMA-positive serum from PBC patients strongly cross-reacts with these xenobiotics. (30)(31) Further experimental support for the role of xenobiotics in PBC pathogenesis comes from the ability of xenobiotics to induce a PBC-like pathology, including AMA, in animal models. (32)(33) The enigma of PBC pathogenesis has been the specific targeting of the biliary epithelial cells in the setting of a ubiquitous autoantigen.…”

Induction of aquaporin 4-reactive antibodies in Lewis rats immunized with aquaporin 4 mimotopes

“…Anergy induction, activation-induced cell death or receptor editing are powerful tolerance mechanisms preventing the formation of autoantibodies in the organism [4]. However, autoantibodies may be induced when such checkpoints of early B cell tolerance are impaired [3], or when they are circumvented by proteins from infectious agents mimicking the antibody targets sufficiently well [11][12][13].…”

“…tuberculosis, different herpes virus infections, Dengue virus infections [9,10], hepatitis, or events summarized as "common cold" and "feverish infection" (for review see [5]). This suggests the action of viral or bacterial proteins mimicking antibody targets as first initiating events, as seen in patients with Guillain Barré Syndrome [11,12] or some other antibody-driven diseases [13,14].…”

Pathogen infections and primary biliary cholangitis

“…This hypothesis is supported by animal studies in which animals immunized with 2OA-BSA developed AMA and autoimmune cholangitis 90,91. Furthermore, cross-reactive monoclonal human antibodies that are reactive to both native PDC-E2 and 2-OA also recognize lipoic acid [92], further suggesting that xenobiotically modified lipoic acid is an initial target of autoimmunity in PBC.…”