[Isolation and characterization of antibodies against chromatin and non-histone proteins from rat thymocytes]

The antisera of rabbits immunized with chromatin and non-histone proteins (NHP) were compared to natural antibodies against chromatin. It was shown that in indirect immunofluorescence and complement fixation assay the immune and control sera interact with chromatin at close dilutions. The IgG purified from the immune sera which do not bind to DEAE-cellulose interact with chromatin at concentrations that are 10-20 times less than that of the corresponding fraction of IgG from intact rabbit serum. The same correlation was observed for the Fab-fragments obtained from immune and control sera IgG. The IgG prepared from the sera of immunized and intact rabbits and eluted from a DEAE-cellulose column with approximately 0.15 M Na-phosphate buffer interact with chromatin at approximately equal concentrations. All the sera tested and the IgG prepared from them interact with NHP but not with DNA and histones, the antibody spectra of immune and control sera being different. It may thus be concluded that intact rabbit sera contain natural antibodies against NHP. Immunization by chromatin or NHP results in generation of antibodies against other fractions of NHP.