Relevance of complement fixing antinuclear antibodies

Abstract

ANA negative cases of SCLE or Sjögren's syndrome may have C-ANAs. A case with Sjögren's syndrome and signs of SLE had both in vivo and in vitro C' fixing ANAs. C-ANA tests can aid in the identification of such cases.

The development of immunofluorescence and the immunopathology of the skin

“…Notably, the group of George Friu 40 and others observed that ANA in rheumatoid arthritis or normal subjects usually fail to react in CIIF tests while sera of active cases of systemic lupus erythematosus do fix complement in CIIF tests. Recent studies also reveal that some patients with other systemic connective tissue diseases such as Sjogren's syndrome may give negative reactions in routine ANA tests but positive ANA in CIIF tests 41 . While immunologists have long recognized that the capacity of antibodies to react with given antigens varies independently from their capacity to fix complement, this important observation merits more explanation and exploration because this demonstrates that the fixation of complement by antigen antibody complexes is not a simple amplifying mechanism and not merely dependent on the isotypes of the antibodies and their subclasses.…”

“…Recent studies also reveal that some patients with other systemic connective tissue diseases such as Sjogren's syndrome may give negative reactions in routine ANA tests but positive ANA in CIIF tests. 41 While immunologists have long recognized that the capacity of antibodies to react with given antigens varies independently from their capacity to fix complement, this important observation merits more explanation and exploration because this demonstrates that the fixation of complement by antigen antibody complexes is not a simple amplifying mechanism and not merely dependent on the isotypes of the antibodies and their subclasses. Complement fixation reveals distinctive antibody properties that play key biologic roles, for example, in the types of immunopathologic effects exercised by autoantibodies.…”