Recently we have shown the presence of catalytically active IgGs, capable to cleave histone H1 and bovine myelin basic protein (MBP), in blood serum of SLE patients. Here we present data that demonstrate the correlation between a) proteolytic activity towards histone H1 and MBP of IgG-antibodies from blood serum of SLE patients and b) disease severity level in these patients. IgGs were isolated from blood serum by chromatography on protein G-sepharose. Commercial preparations of bovine myelin basic proteins (MBP) and calf thymus histone H1 were used as substrates. Analysis of the proteolytic activity showed that 16 of 38 lgG-preparations (42,1%) obtained from blood serum of SLE patients were capable of cleaving both histone H1 and MBP with different efficiency. It was revealed that the presence in blood serum of lgGs possessing proteolytic activity towards both histone H1 and bMBP closely correlates with manifestation of the disease severity in SLE patients.

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