ABSTRACT Recently we have shown that blood serum of some SLE patients contains IgG-antibodies capable of hydrolyzing both calf thymus histone H1 and bovine myelin basic protein (bMBP); however this proteolytic activity was not detected in sera of healthy donors. In this work, we demonstrate that secretory IgA (sIgA), shown to be homogenous by electrophoresis and HPLC-SEC, and able to hydrolyze both calf thymus histone H1 and bMBP, are present in colostrum of healthy mothers. sIgAs purified from colostrums by sequential chromatography on Protein A-Sepharose and DEAE-Fractogel were able to cleave both histone H1 and bMBP. Such enzymatic activity was shown to be an intrinsic property of the sIgA molecule, since it was preserved during size exclusion chromatography at acidic pH. sIgAs proteolytically active toward both proteins were also purified by the affinity chromatography on Histone H1-Sepharose and bMBP-Sepharose columns. Protease activity of sIgA-abzymes was shown to be inhibited by serine protease inhibitors. Potential biological role of sIgA-abzymes in human milk of healthy mothers is discussed.
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