Abstract
AbstractAbsence of C2 was identified in an 18‐year‐old white male with progressive and rapidly fatal lupus nephritis. Genetic studies of the patient and 8 family members linked this deficiency with the HLA haplotype A10/B18, for which the patient was homozygous. High titers (1:1600) of anti‐RNP antibodies, as well as antibodies to double‐stranded DNA, were present. Serum levels of properdin factor B were persistently decreased, whereas levels of C1q and C3 intermittently were low. Biopsies of skin and kidney showed typical SLE histopathology with deposition of immunoglobulins and early‐ and late‐acting C components; properdin was deposited in the kidney. Despite the inability of the patient's serum to mediate lysis through the classic C pathway, C‐dependent lysis through the alternative pathway was readily achieved using either unsensitized rabbit cells in gels or mixtures of guinea pig cells and zymosan as the indicator system. These studies thus reveal a new association of fatal lupus nephritis with homozygous C2 deficiency and show the usefulness of two new assays for measuring the hemolytic capacity of the alternative C pathway in human serum. The decreased levels of properdin factor B in serum, deposition of properdin and C3 in renal tissue, and capacity of C2‐deficient serum to mediate hemolytic C activity through the properdin pathway in vitro implicate the alternative C pathway in the severe tissue damage observed.
Published Version
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