SPECIFICITY OF MONOCLONAL ANTI-NUCLEOSOME AUTOANTIBODIES DERIVED FROMLUPUS MICE

Recently, anti-nucleosome antibodies, which do not bind to DNA or to i ndividual histones, have been identified in longitudinal studies in lu pus mice. These anti-nucleosome antibodies occur early in spontaneous SLE and are formed prior to other anti-nuclear specificities. However, nucleosomal epitopes are yet to be fully characterized. We selected a panel of six monoclonal anti-nucleosome antibodies (mAbs) (#2, #32, # 34, PL2-6, LG8-1 and LG10-1) derived from lupus mice. These mAbs were tested in ELISA on subnucleosome structures and on a panel of 53 histo ne peptides, covering the entire sequence of the five histones. Two mA bs reacted with one of these peptides, but the reactivity hardly excee ded the background reactivity. Based on the nucleosome and subnucleoso me ELISA we identified different recognition patterns. Three mAbs show ed the highest reactivity towards the intact nucleosome. For two of th em (#32 and LG8-1) the nucleosomal epitope was primarily located on H2 A-H2B/DNA, whereas for mAb #34 this primary epitope was located on H3/ H4/DNA. Two mAbs (#2 and PL2-6) showed the highest reactivity with H2A -H2B/DNA and one mAb (LG10-1) recognized H3-H4/DNA. In the subnucleoso me ELISA all but one (mAb #32) recognized more than one epitope, inclu ding DNA complexed to a variety of cationic molecules. Comparing these reactivities we identified for all mAbs one specific nucleosomal epit ope, whereas reactivity with other subnucleosomes was comparable to th e reactivity towards DNA complexed with cationic molecules. In inhibit ion experiments both in ELISA and in immunofluorescence it was found t hat only one of the mAbs (i.e. PL2-6), recognizing an epitope on H2A-H 2B/DNA as primary epitope, could be inhibited by H2A-H2B/DNA in fluid phase. The two mAbs recognizing an epitope on H3-H4/DNA as primary epi tope could be inhibited by H3-H4/DNA in fluid phase. From these analys es, we conclude first that for these nucleosome specific mAbs linear h istone peptides are not Fiery important. Second, that these mAbs all r ecognize different epitopes on both H2A/H2B-DNA and H3/H4-DNA and thir d that some solid phase H2A/H2B-DNA epitopes are not expressed on flui d phase H2A/H2B-DNA. Our findings suggest that in SLE the nucleosome c an act as auto-antigen and that there is no immunodominant beta cell e pitope within the nucleosome. (C) 1996 Academic Press Limited