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Hereditary dysfunction of the third component of complement associated with a systemic lupus erythematosus-like
U R Nilsson1, B Nilsson, K E Storm
1Department of Clinical Immunology and Transfusion Medicine, University Hospital, Uppsala, Sweden.
Objective:
We describe a dysfunction of C3 in a patient with a systemic lupus erythematosus (SLE)-like syndrome. Alternative pathway complement function was absent, but classical pathway complement function was partially intact.
Methods:
We used functional, preparative, and immunochemical techniques in the study.
Results:
The patient's C3 proved normally susceptible to trypsin proteolysis and partially resistant to classical pathway, but completely resistant to alternative pathway, convertase-dependent cleavage.
Conclusion:
The dysfunction, thus, was caused by a failure of C3 to interact with the C3 convertases, rather than by a lack of a proteinase-sensitive cleavage site in the deficient protein.