No abstract

The human milk secretory immune system is the first line of protection for the newborn infant against various pathogens. Secretory IgA (sIgA), the typical immunoglobulin found in secretions, can fight infections through many mechanisms. Using different methods, we have shown that sIgA from the milk of healthy women possesses DNAse and RNAse activities. The catalytic center is localized in the light chain of catalytic sIgA, while the DNA-binding center is predominantly formed by its heavy chain. The enzymic properties and substrate specificity of catalytic sIgA distinguish it from other known DNases and RNases. It is reasonable to assume that the milk DNA- and RNA-hydrolyzing antibodies are capable not only of neutralizing viral and bacterial nucleic acids by binding these antigens as well as by hydrolyzing them. The DNA-hydrolyzing activity of Abs raises the possibility that these catalytic Abs may provide protective functions for the newborn through the hydrolysis of viral and bacterial nucleic acids.

In human milk we previously found catalytic antibodies (abzymes) catalyzing hydrolysis of DNA, RNA, NMP, NDP, and NTP and also phosphorylation of proteins and lipids. In the present study we have analyzed nuclease activities of antibodies in blood of women during pregnancy and lactation. Blood of healthy male and female volunteers lacked catalytically active antibodies, whereas antibodies from blood of pregnant women hydrolyzed DNA and RNA and their relative activity varied over a wide range. Relative blood abzyme activities significantly increased after delivery and at the beginning of lactation. The highest abzyme activity was observed in blood of parturient women. Although the dynamics of changes in antibody DNase activity during pregnancy was rather individual for each woman, there was a common trend in the increase in antibody activity in the first and/or third trimester of the pregnancy. The DNase activity of IgG and IgM from blood of healthy pregnant women was 4-5 times less than that from pregnant women with pronounced autoimmune thyroiditis.