Immune responses to peptides containing homocitrulline or citrulline in the DR4-transgenic mouse model of rheumatoid arthritis

J Autoimmun. 2018 May;89:75-81. doi: 10.1016/j.jaut.2017.12.002. Epub 2017 Dec 11.


Antibodies to proteins/peptides containing citrulline are hallmarks of Rheumatoid Arthritis (RA). These antibodies are strongly associated with the expression of the Shared Epitope (SE). RA patients also generate antibodies to homocitrulline-containing proteins/peptides (also referred to as anti-carbamylated protein antibodies (Anti-CarP)). This study was undertaken to investigate the relationship between homocitrulline and citrulline immune responses using an established mouse model of RA: DR4-transgenic (DR4tg) mice that express the human SE. C57BL/6 (B6) and DR4tg (on a B6 background) mice were immunized subcutaneously with a homocitrullinated peptide (HomoCitJED). Splenic T cell proliferation was evaluated by 3H-thymidine incorporation assay. Antibodies to homocitrullinated and citrullinated antigens were screened by enzyme-linked immunosorbent assay (ELISA). Antibody cross-reactivity was examined by inhibition with HomoCitJED and its citrullinated counterpart peptide, CitJED (the number of homocitrullines in HomoCitJED is equal to the number of citrullines in CitJED). HomoCitJED-immunized DR4tg mice developed early T and B cell responses to HomoCitJED and late responses to CitJED. These mice also developed anti-CCP2 antibodies. In some mice, antibodies to HomoCitJED were also reactive to CitJED. B6 mice immunized with HomoCitJED developed late T and B cell responses to HomoCitJED, but did not generate responses to citrullinated antigens. Unlike DR4tg mice, anti-HomoCitJED antibodies from B6 mice did not react to CitJED. In conclusion, DR4tg mice immunized with HomoCitJED developed immune responses to CitJED, indicating cross-reactivity. CitJED immune responses were dependent on the SE. HomoCitJED responses occurred in the absence of the SE (B6 mice); however, they developed earlier in DR4tg SE-expressing mice.

Keywords: Anti-citrullinated protein/peptide antibodies; Anti-homocitrullinated (carbamylated) protein/peptide antibodies; Cross-reactivity; Mouse model; Rheumatoid arthritis; Shared Epitope.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Citrullinated Protein Antibodies / metabolism
  • Arthritis, Rheumatoid / immunology*
  • Citrulline / analogs & derivatives*
  • Citrulline / immunology*
  • Disease Models, Animal
  • Epitopes / immunology*
  • Female
  • Histocompatibility Antigens Class II / genetics
  • Humans
  • Immunity, Humoral
  • Immunization
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Peptides / immunology*


  • Anti-Citrullinated Protein Antibodies
  • Epitopes
  • Histocompatibility Antigens Class II
  • Peptides
  • homocitrulline
  • Citrulline

Grant support