Complete functional C1q deficiency associated with systemic lupus erythematosus (SLE)

Abstract

SUMMARY A complete functional deficiency of Clq is described in a patient suffering from SLE. From reduced plasma C1 activity of the parents a hereditary trait was assumed. The defective C1q molecule was haemolytically inactive, did not bind to immune complexes, and was not recognized by the monocyte C1q receptor. C1 activity in the patient's serum could be restored by the addition of purified C1q. Analysis by gelfiltration and ultracentrifugation experiments revealed an immunoreactive molecule of about 150 kD mol. wt, corresponding to one structural subunit of the C1q macromolccule, containing two A chain-B chain dimers and a C-C chain dimer. Applying Southern blot analysis with cDNA clones encoding for the three individual chains of the C1q molecule, no restriction fragment length polymorphism was detected, ruling out possible major alterations of the genetic information.