Detection of nucleosome particles in serum and plasma from patients with systemic lupus erythematosus using monoclonal antibody 4H7

Objective. To develop a monoclonal antibody reagent that would react with n ucleosomes but not directly with constituent double stranded DNA (dsDNA) or with histones. Methods. Mice were immunized with highly purified chicken mononucleosomes a nd hybridomas employed to produce Mab that did not react with dsDNA or hist ones but still showed reactivity with nucleosomes. Results. Murine monoclonal IgG antibody 4H7, generated from a mouse immuniz ed with highly purified chicken erythrocyte nucleosomes, showed no direct E LISA reactivity with either dsDNA or isolated histones or with Sm and RNP a ntigens or combinations of any of these components. Mab 4H7 did show strong ELISA reactivity for chicken erythrocyte and calf thymus nucleosomes as we ll as for human leukocyte nucleosomes. The Mab did show strong ELISA reacti ons with peptides 1-25 of histone H2B and 1-21 of H3, which correspond to s equences known to be located at the surface of nucleosomes. We then measure d relative serum levels of 4H7 reactive nucleosome antigen in 140 patients with systemic lupus erythematosus (SLE) in parallel with 50 non-SLE patient s with other types of connective tissue disease and 92 healthy subjects. Oc casional low levels of serum nucleosomal antigen were seen in 4 of 92 contr ols. but many patients with SLE (66/140) showed marked elevations of serum nucleosomal antigen. No difference was observed when serum or plasma sample s were studied. A marked correlation (R = 0.401, p < 0.0001) was noted when disease activity score (SLEDAI) was plotted against optical density value measured with 4H7 in ELISA. Further, the levels of circulating nucleosomes were raised in SLE patients with very active central nervous system and ren al involvement. Conclusion. Presence of nucleosome related antigen in sera from patients wi th SLE may provide insight into the sequence of disease related antigenic s timuli in active SLE.