Cell wall beta-glucan derived from Candida albicans acts as a trigger for autoimmune arthritis in SKG mice

SKG mice are a recently established experimental model for rheumatoid arthritis (RA). Although they spontaneously develop chronic autoimmune arthritis under conventional conditions, SKG mice failed to develop chronic arthritis in a strictly controlled specific pathogen-free (SPF) environment. Beta-glucan (BG) from Laminaria digitata, laminarin (LAM), induced arthritis under SPF conditions, thus BG would be a pathogenic factor for arthritis in SKG mice. Therefore, we prepared BG from Candida albicans, a pathogenic fungus and investigated whether BG from C. albicans induced arthritis in SKG mice under SPF conditions. SKG mice were injected intraperitoneally with particulate BG (oxidative-Candida albicans (OX-CA)), soluble BG (Candida soluble beta-glucan (CSBG)) from C. albicans and LAM as a positive control. In addition, schizophyllan (SPG) from Schizophyllum commune or Mycobacterium whole cells were injected into SKG mice to induce arthritis. Mice injected with OX-CA, CSBG and SPG had more severe arthritis than with LAM, and whole Mycobacterium cells. IL-6 concentration in sera from SKG mice injected with OX-CA or CSBG was high, whereas not detected in sera from mice treated with LAM. In histological analysis, infiltration of inflammatory cells was observed in SKG mice injected with BG. These results suggest that fungal infection may be a factor to induce and exacerbate autoimmune diseases such as RA.