Relevance of complement fixing antinuclear antibodies

Background Connective tissue diseases (CTDs) are a heterogeneous group of d isorders defined by the association of a variety of clinical manifestations with immunologic and other laboratory findings, Overlap of syndromes and a berrant findings appear rather frequently. Methods Sera of eight antinuclear antibody (ANA) negative, cases of subacut e cutaneous lupus erythematosus (SCLE) with antibodies to Ro (SS-A) and a n inth case with clinical and laboratory signs of Sjogren's syndrome and syst emic lupus erythematosus (SLE) were tested for complement (C') fixing antin uclear antibodies (C-ANAs). The ninth case was examined in depth by direct immunofluorescence (DIF) and a two-step "C + DIF" test of biopsies for C' f ixation to in vivo bound ANAs, as well as serum tests for C-ANA, ANA, and S CLE markers. Results Sera of five of the eight ANA negative, Ro(SS-A) positive SCLE case s had C-ANAs. The ninth case. a 50-year-old woman with clinical and laborat ory signs of Sjogren's syndrome and SLE, gave a strong positive C + DIF rea ction in the skin biopsy for in vivo bound ANAs that fix C', but negative A NAs and C-ANAs in routine serum tests; they revealed antimitochondrial anti bodies, Serum tests on normal skin, however, revealed weak ANA and strong C -ANA reactions with in vitro fixed C'. Conclusions ANA negative cases of SCLE or Sjogren's syndrome may have C-ANA s. A case with Sjogren'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 cas es.