Histopathology of arthritis joints. Representative hematoxylin and eosin sections of hind paws obtained from adjuvant-induced arthritic animals treated with intra-articular injections of 'no treatment' (No-tr) (A), saline (SA) (B), and hyaluronan (HA) (C). In rats in the No-tr group, in which cartilaginous tissue could not be clearly detected, bone damage was even greater and massive inflammatory cells infiltrated the synovium (a). Similar changes were observed in rats treated with SA. Cartilage erosion was more pronounced and the extensively expanded synovial pannus was more densely infiltrated with mononuclear cells (b). In rats treated with HA, the joints were much less inflamed, and lymphocyte accumulation (c) and cartilage damage decreased. There was no sign of bone destruction. 1D, one dose; 3D, three doses; 3D6d, follow-up at the 6th day after three doses; cart, cartilage; syn, synovial tissue.