Conformational changes in C1q after binding to immune complexes: detection of neoantigens with monoclonal antibodies.

The formation of neoantigens within the C1q molecule after the binding of C1r and C1s to C1q and the binding of C1q to immune complexes is described. The neoantigens were detected by different monoclonal anti-C1q antibodies. This immunochemical study supports the hypothesis drawn from functional studies that the activation of the classical C pathway results from conformational changes within the C1q molecule leading to the activation of C1r and subsequently C1s.