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Activation of the Classical Complement Pathway by Nephritic Factor Bound to the Alternative Pathway C3/C5 Convertase^{1 ,2}

From the Department of Molecular Immunology, Research Institute of Scripps Clinic, La Jolla, California 92037

Abstract

Nephritic Factor (NF), the potent alternative pathway activator, which is occasionally found in association with certain types of nephritis has recently been identified as an IgG class autoantibody specific for the C3 convertase
of the alternative pathway. In these studies we have examined the possibility that the cell-bound NF-stabilized C3 convertase
binds and activates the first component of the classical pathway of complement.
bound C1q, and the extent of binding was dependent upon the number of NF molecules bound per cell and decreased parallel to the dissociation and release of NF from the cells. Interaction of C1 with bound NF resulted in its activation as shown by the proteolytic conversion of proenzyme C1s to its activated form C1. As was the case with C1q binding, C1 activation was dependent on the number of NF molecules bound per cell. Thus the NF-stabilized C3 convertase binds and activates C1.

Footnotes

¹ This is publication No. 1573 from the Research Institute of Scripps Clinic. This work was supported by Public Health Service Grants CA 14692 and SO7 RR 05514 and Program Project Grants AI 07007 and HL 1644.

² Presented in part at the 62nd annual meeting of the American Association of Immunologists, Atlanta, Georgia, June 1978 (1).

³ Visiting Investigator from Hôpital Henri-Mondor, Creteil, France. Supported by DGRST and INSERM, Paris, France.

⁴ Recipient of Established Investigatorship (AHA 77 202) of the American Heart Association. Correspondence should be addressed to: Robert D. Schreiber, Ph.D.