Escherichia coli heat‐labile enterotoxin B subunit prevents autoimmune arthritis through induction of regulatory CD4+ T cells

Objective The receptor‐binding B subunit of Escherichia coli heat‐labile enterotoxin (EtxB) is a highly stable, nontoxic protein that is capable of modulating immune responses. This study was conducted to determine whether mucosal administration of EtxB can block collagen‐induced arthritis (CIA) and to investigate the mechanisms involved. Methods Clinical arthritis in DBA/1 mice was monitored following mucosal administration of EtxB on 4 occasions. The dependence of disease prevention on receptor binding by EtxB and the associated alterations to the immune response to type II collagen (CII) were assessed. Adoptive transfer experiments and lymph node cell cocultures were used to investigate the underlying mechanisms. Results Both intranasal and intragastric delivery of EtxB were effective in preventing CIA; a 1‐μg dose of EtxB was protective after intranasal administration. A non–receptor‐binding mutant of EtxB failed to prevent disease. Intranasal EtxB lowered both the incidence and severity of arthritis when given either at the time of disease induction or 25 days later. EtxB markedly reduced levels of anti‐CII IgG2a antibodies and interferon‐γ (IFNγ) production while not affecting levels of IgG1, interleukin‐4 (IL‐4), or IL‐10. Disease protection could be transferred by CD4+ T cells from treated mice, an effect that was abrogated upon depletion of the CD25+ population. In addition, CD4+CD25+ T cells from treated mice were able to suppress anti‐CII IFNγ production by CII‐primed lymph node cells. Conclusion Mucosal administration of EtxB can be used to prevent or treat CIA. Modulation of the anti‐CII immune response by EtxB is associated with a reduction in Th1 cell reactivity without a concomitant shift toward Th2. Instead, EtxB mediates its effects through enhancing the activity of a population of CD4+ regulatory T cells.