• ankylosis;
  • enthesitis;
  • MRL/lpr;
  • rheumatoid arthritis;
  • rheumatoid factor;
  • seronegative;
  • synovitis

Based on the hypothesis that the complex pathological and immunological manifestations of rheumatoid arthritis (RA) and the related diseases are under the control of multiple gene loci with allelic polymorphism, a recombinant congenic mouse strain was prepared between an MRL/Mp-lpr/lpr (MRL/lpr) strain, which develops arthritis resembling RA, and a non-arthritic strain C3H/HeJ-lpr/lpr (C3H/lpr). In MRL/lpr × (MRL/lpr × C3H/lpr) F1 mice, the mice developing severe arthritis were selected based on joint swelling to further continue intercrosses, and then an McH-lpr/lpr-RA1 (McH/lpr-RA1) strain was established and its histopathological phenotypes of joints and autoimmune traits were analyzed. Arthritis in McH/lpr-RA1 mice developed at a higher incidence by 20 weeks of age, compared with that in the MRL/lpr mice, who had severe synovitis (ankle, 60.3%; knee, 65.1%), and also fibrous and fibrocartilaginous lesions of articular ligamenta resembling enthesopathy (ankle, 79.4%; knee, 38.1%), resulting in ankylosis. The lymphoproliferative disorder was less, and serum levels of IgG and IgG autoantibodies including anti-dsDNA and rheumatoid factor were lower than those of both MRL/lpr and C3H/lpr strains. McH/lpr-RA1 mice may provide a new insight into the study of RA regarding the common genomic spectrum of seronegative RA and enthesopathy.