Variability of Substrate Specificity of Serum Antibodies Obtained from Patients with Different Autoimmune and Viral Diseases in Reaction of tRNA Hydrolysis.

Recently we have shown that the substrate specificity of catalytic IgG isolated from sera of patients with Hashimoto's thyroiditis, systemic lupus erythematosus (SLE), polyarthritis and hepatitis B for classic poly(N) homopolynucleotide substrates and for specific tRNA(Phe) with compact and stable structure was correlated with the type of disease. At the same time the cleavage specificity was different in comparison with that of all known human RNases. Here we investigated for the first time the hydrolysis by the IgGs isolated from sera of 31 patients with different diseases of the in vitro transcript of human mitochondrial tRNA(Lys) which has less stable structure as compared to tRNA(Phe). The level of activity was strongly dependent on the patient, but in general increased in the order: hepatitis B </= Hashimoto's thyroiditis < SLE. The pH dependencies and various salts effects also varied for Abs from the sera of different patients. Nevertheless, the RNase activity of all IgGs was specifically stimulated by Mg(2+) ions, that essentially completely suppress the activity of all known human RNases. In contrast to the classical substrates, no correlation between patient's IgG cleavage specificity and a specific disease was revealed; each patient demonstrated an individual repertoire of polyclonal RNA-hydrolyzing IgGs independently of the disease.