Antichromatin antibody positivity Anti-nucleosome antibody positivity 2026-08-10T08:57:55Z The term nucleosome defines a basic unit of chromatin. Each nucleosome consists of 146 base pairs of double stranded DNA, wrapped twice around a histone octamer, a protein core. A histone octamer consists of two molecules each of histones H2A, H2B, H3, and H4. In a chromatin, nucleosomes are connected by 15-80 base pairs of linker DNA, to which histone H1 is attached. Anti-dsDNA and anti-histone antibodies (AHA) belong to the nucleosome family as do anti-nuc specific antibodies, since nucleosomes share several common epitopes with dsDNA and histones. Nucleosome specific antibodies do not react with the individual components of the nucleosome, that is, DNA and histones, but recognize conformational epitopes resulting from interactions between the DNA and histone. The presence of autoantibodies (immunoglobulins) in the blood circulation that are directed exclusively (or predominantly) against nucleosomes or subnucleosomal structures, consisting of DNA plus core histones.