KRN/I-A^g7 Mouse Arthritis Is Independent of Complement C3

KRN/I-A(g7) (KxB/N) is a mouse model of inflammatory arthritis, which resembles human rheumatoid arthritis. Arthritis in these animals is caused by autoreactivity to a ubiquitously expressed autoantigen, glucose-6 phosphate isomerase. Tolerance is broken at both the T cell and B cell level. The sera from KRN/I-A(g7) mice can induce mouse arthritis in healthy mice. Complement components of the alternative complement pathway, including C3, have been shown to be required in induction of mouse arthritis by serum transfer. We have bred KRN/I-A(g7) mice onto a C3-deficient background and followed cohorts for the spontaneous appearance of arthritis. We have also transferred KxB/N serum to B6.I-A (g7) recipients. C3-deficient KRN/I-A(g7) mice spontaneously developed severe, destructive arthritis, comparable to that seen in C3-intact KRN/I-A(g7) mice. However, serum transfer experiments confirmed the strong requirement for C3 in the passive model. The pathogenesis of spontaneous KRN/I-A(g7) arthritis can largely proceed by complement-independent pathways and must have pathology effector mechanisms in addition to those seen in the passive serum transfer model.