The progress in identifying immunological mechanisms in juvenile idiopathic arthritis (JIA) has partly been hampered by the fact that the disease is heterogeneous. Here we have investigated complement and Fc receptors, as part of the inflammatory process, in two subgroups of JIA.
Blood from 26 patients with oligoarticular or polyarticular course type JIA and 21 healthy age and sex-matched controls were investigated by FACS and immunoassays.
Increased numbers of monocytes and augmented plasma levels of C-reactive protein, C3a and IgG were found in both JIA subgroups. However, only polyarticular patients exhibited increased expression of Fc gamma receptor (FcγR) II and III and complement receptor (CR) 1 on monocytes along with enhanced CR1 expression on B cells. A correlation was observed between degree of receptor expression and C3a levels in the patients.
Complement and Fc receptors are up regulated in children with multiple joint involvements, thus highlighting these pathways in the pathogenesis of polyarticular JIA.