New Zealand white rabbits immunized with RNA-complexed total histones develop an autoimmune-like response.

The antibody response of rabbits immunized with a total histone mixture containing randomly coiled H1/H5, H2A, H2B, H3 and H4 devoid of DNA was investigated in direct and competitive ELISA. The antisera were tested with isolated histones and chromatin and with a series of overlapping synthetic peptides covering the entire sequences of the four core histones and two peptides of H1. It was found that the New Zealand (NZ) white rabbits immunized with the total histone (TH) mixture complexed with RNA produced IgG antibodies reacting with histones and with a number of histone peptides but not with chromatin. The antisera also contained IgG antibodies which bound components that correspond to common target antigens in autoimmune diseases such as native dsDNA, peptides of Sm-D antigen, ubiquitin, branched peptides of ubiquitinated H2A and poly(ADP-ribose). By competition experiments, it was shown that these antibodies corresponded to non-crossreacting antibody populations. New Zealand rabbits immunized with TH in the absence of RNA or random outbred rabbits immunized with the RNA-complexed histone fraction produced antibodies reacting with histone, chromatin and very few histone peptides, while no activity with non-related antigens was observed. The pattern of reactivity of antisera raised in NZ rabbits with RNA-complexed TH was found to be very similar to that observed in sera of patients with systemic lupus erythematosus while, in contrast, the antibody response was very different in NZ or outbred rabbits immunized with various native nuclear particles and with individual histones. Altered nucleosome particles rather than native nucleosomes may represent the antigenic stimulus giving rise to autoantibodies.