Lupus nephritis sera contain autoantibodies that recognize epitopes within the globular fragment of C1q.

High levels of autoantibodies to some complement proteins are detected in the sera of SLE patients. Anti-C1q autoantibodies make a great part of them. Their presence is associated with renal involvement, in particular with lupus nephritis (LN) and the titre of these autoantibodies correlates with the clinical activity of the disease. We analysed by ELISA 18 SLE sera with biopsy-proved LN for the presence of autoantibodies against the globular fragment of C1q using recombinant globular head regions of A, B and C chains of human C1q (ghA, ghB and ghC, respectively). For reference we analysed the sera from 62 healthy volunteers. The recombinant proteins were used as test-antigens to evaluate the levels of autoantibodies specific for ghA, ghB and ghC. LN sera, containing high levels of anti-C1q antibodies, showed differential increased binding to ghA, ghB and ghC.