Antibodies in rabbits immunized with cationized IgG react with histones H3 and H4

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Abstract
Objective. Rabbits immunized with cationized rabbit IgG develop antinuclear antibodies. This study was aimed at identifying the reactive antigens.Methods. Rabbits were immunized with homotypic or allotypic IgG that were physicochemically altered to produce positively charged dimethylpropanamide (polycationic) side chains.Results. Seven of 11 rabbits injected with cationized IgG produced antinuclear antibodies detected by indirect immunofluorescence. By enzyme‐linked immunosorbent assay, these were IgG antibodies reacting with histone (H3–H4)2 tetramer and with individual histone polypeptides H3 and H4. The antihistone antibodies were absorbed by cationized IgG but not by normal IgG.Conclusion. Cationized IgG appears to possess antigenic determinants of sufficient similarity to produce antibody responses cross‐reactive with histones H3 and H4.