Secretory immunoglobulin A from healthy human mothers' milk catalyzes nucleic acid hydrolysis

The human milk secretory immune system is the first line of protection for the newborn infant against various pathogens. Secretory IgA (sIgA), the typ ical 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 c enter is predominantly formed by its heavy chain. The enzymic properties an d substrate specificity of catalytic sIgA distinguish it from other known D Nases and RNases. It is reasonable to assume that the milk DNA- and RNA-hyd rolyzing antibodies are capable not only of neutralizing viral and bacteria l nucleic acids by binding these antigens as well as by hydrolyzing them. T he DNA-hydrolyzing activity of Abs raises the possibility that these cataly tic Abs may provide protective functions for the newborn through the hydrol ysis of viral and bacterial nucleic acids.