Anti-histone H1 IgGs possess proliferative activity towards human T-leukaemia CEM cells.

The aim of this study was to characterize the proliferative activity of the anti-histone H1 IgGs towards human T-leukaemia CEM cells. MATERIALS AND METHODS: Anti-histone H1 IgGs were purified from blood serum of systemic lupus erythematosus patients by precipitation of serum proteins with 50% ammonium sulfate followed by a sequential affinity chromatography on Protein G-Sepharose and histone H1-Sepharose columns. To avoid contamination with other proteins, anti-histone H1 IgGs were subjected to strongly acidic pH 2.0 during gel filtration through HPLC column. The effects of the anti-histone H1 IgGs on cell viability and cell cycle were tested by MTS-assay and flow cytometry, correspondingly. The cross-reactivity of the anti-histone H1 antibodies towards heterogenetic and cellular antigens was evaluated by Western-blot analysis. RESULTS: It was found that incubation of CEM cells with the HPLC-purified anti-histone H1 IgGs resulted in significant stimulation of cell growth by 46% after 48 h of incubation. These IgGs possess an antigenic poly-specificity to positively charged heterogenetic antigens and different cellular antigens. FITC-labeled and biotinylated anti-histone H1 IgGs are internalized by CEM cells and preferentially accumulated in the cytoplasm. CONCLUSION: The anti-histone H1 IgGs are shown to internalize human T-leukemia CEM and stimulate their proliferation. These IgGs are polyspecific toward cellular antigens.

[Proteolytic activity of IgG-antibodies of mice, immunized by calf thymus histones].

The main goal of the study was to determine the ability of histones to induce production of the proteolytically active IgG-antibodies in BALB/c mice. In order to perform this study 8 mice were immunized with the fraction of total calf thymus histones. IgGs were isolated from the serum of the immunized and not immunized animals by means of precipitation with 33% ammonium sulfate, followed by affinity chromatography on protein G-Sepharose column. Histones, myelin basic protein (MBP), lysozyme, BSA, ovalbumin, macroglobulin, casein and cytochrome c served as substrates for determining the proteolytic activity. It was found that IgGs from the blood serum of immunized mice are capable of hydrolyzing histone H1, core histone and MBP. On the contrary, the proteolytic activity of IgGs from the blood serum of not immunized mice was not detected. The absence of proteolytical enzymes in the fraction of IgGs was proven by HPLC chromatography. High levels of proteolytic activity toward histones have been also detected in affinity purified IgGs from blood serum of patients with rheumatoid arthritis, but not in healthy donors. These data indicate that eukaryotic histones may induce production of protabzymes in mammals. The possible origin of these protabzymes and their potential biological role in mammalians is discussed.

[Proteolytic activity of blood serum IgG in patients with systemic lupus erythematosis].

Proteolytic activity of blood serum IgGs of 10 patients with systemic lupus erythematosis (SLE) was studied in comparison with such activity in 10 clinically healthy donors. Antibodies were precipitated from blood serum by saturation with 50% (NH4)2SO4 and IgG was isolated by the affinity chromatography on protein G-sepharose column. Histone H1 and core histones from the calf thymus, bovine myelin basic protein (MBP), lysozyme of chicken egg and bovine serum albumin (BSA) were used as substrates for proteolytic action. It was found that 4 of 10 preparations of IgGs possess an ability to hydrolyze both histone H1 and MBP. These antibodies practically did not cleave lysozyme of the chicken egg and BSA. Gel-filtration of antibodies under acidic condition and following examination of proteolytic activity of chromatographic fractions showed that histone H1 and MBP-hydrolyzing activity is attributable to IgG-antibodies. Thus, the presence of catalytically active antibodies (protabzymes) in the blood serum of patients with SLE has been demonstrated. Their origination and biological role are discussed.