Epitope spreading of Lyme autoantigen apoB-100 and CD4+ T cell responses toBorrelia burgdorferiMcp4 are regulated by IL-10 in murine Lyme disease

Abstract

Borrelia burgdorferi, the causative agent of Lyme disease (LD), has evolved immune evasion mechanisms to establish a persistent infection in their vertebrate hosts, resulting in chronic inflammation and autoimmune T and B cell reactivity in many B. burgdorferi-infected individuals. In this study, we used an unbiased immunopeptidomics approach to identify foreign and self MHC class II peptides isolated from inguinal and popliteal lymph nodes from B. burgdorferi-infected C57BL/6 (B6) mice, which develop mild, self-limiting LD; and from infected B6 Il10-/- mice, which develop severe, persistent LD. Nearly 10,000 MHC-II peptides were identified by LC-tandem MS analysis which included many peptides derived from proteins abundant in arthritic joints that are associated with inflammation, tissue repair, and extracellular matrix remodeling. Notably, the number and variety of unique peptides derived from apolipoprotein B-100 (apoB-100); a validated autoantigen in human Lyme arthritis (LA), atherosclerosis, and liver disease; was greatly expanded in lymph nodes of infected mice, particularly in Il10-/- mice at 4 weeks (6-fold increase) and 16 weeks (15-fold increase) post-infection, compared with uninfected mice, indicating epitope spreading. One of the apoB-100 peptides identified in infected, but not uninfected, B6 and Il10-/- mice was APOB3500-3515, an immunogenic cryptic epitope in murine autoimmune atherosclerosis. No apoB-100 peptides had sequence homology to any B. burgdorferi antigens. Surprisingly, only six peptides derived from B. burgdorferi proteins were validated in this study. One of these B. burgdorferi epitopes, derived from methyl-accepting chemotaxis protein Mcp4 (BB0680), was an immunogenic target of CD4+ T cell responses in B. burgdorferi-infected Il10-/- mice, but not in B6 mice. In conclusion, this study has shed light on the importance of IL-10 in suppressing epitope spreading and limiting B. burgdorferi-specific CD4+ T cell responses. Furthermore, this study supports epitope spreading and exposure of cryptic antigens as likely mechanisms of infection-induced apoB-100 autoimmunity in LD.