Complement‐activating abilities of defined antinuclear antibodies

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Abstract
A complement‐fixing immunofluorescence assay on HEp‐2 cells was used to assess the ability of various antinuclear antibodies (ANA) to activate complement. Sera which contained only specific antibodies to nuclear RNP, SS‐B/La, centromere, Sm antigen, double‐stranded DNA, and/or nuclear histone were selected. Relative abilities of various ANA to activate complement were determined from the ratio of titers of C3, C4, or properdin‐fixing ANA to the IgG ANA titers. Nuclear RNP‐anti‐RNP complexes activated and deposited significantly more complement C3 than other ANA (P < 0.02). Antibodies to SS‐B/La, centromere, and Sm activated more complement than anti‐DNA or antihistone (P < 0.02). Antihistone antibodies activated the least complement. These studies demonstrate that different ANA have significantly different orders of complement‐activating capabilities when bound to their respective nuclear antigens.