Immunization of DBA/1 mice with glucose-6-phosphate-isomerase-derived peptides induces arthritis. (a) Mice were immunized with either 400 μg glucose-6-phosphate-isomerase (G6PI), 50 μg G6PI85–99, 50 μg G6PI325–339 or 50 μg G6PI469–483 in complete Freund's adjuvant. Shown is the clinical severity of disease in arthritic mice in a representative experiment (n = 5 per group). Each peptide was tested in at least two independent experiments (Table 1). (b) The animals immunized with G6PI showed a strong synovialitis (circles) and inflammation of the adjacent skeletal muscle (star), which was dominated by neutrophilic granulocytes (small arrow) as a sign of acute inflammation and exhibited activation of synovial fibroblasts to a lesser extent (broad arrow). The synovial tissue was enlarged due to the dense inflammatory infiltrate; however, bone destruction was only focally observed. Similar but markedly less intense alterations could be observed in the animals immunized with G6PI85–99, whereas immunization with peptide G6PI469–483 resulted in an inflammation that was as strong as when using whole G6PI. (H & E; original magnification: upper row, 50×; lower row, 200×). Results show representative data from at least nine individual mice from two typical experiments.