P. histicola ↓ incidence of arthritis; ↓ severity of arthritis; ↓ IL-2; ↓ IL-17; ↓ TNF; ↑ IL-4; ↑ IL-10; ↓ anti-CII antibodies; ↓ gut permeability; ↑ ZO-1. This evidence concerns the gene IL17A and arthritic joint disease.