Secretory immunoglobulins A from human milk possess affinity to oligonucleotides and nucleic acids

The antibody (AB) fraction containing sIgA and IgG was isolated from human milk by Protein A-Sepharose chromatography and was shown to possess affinity to DNA-cellulose. Ion-exchange HPLC of these AB on a TSK DEAE-5PW column resulted in the isolation of a fraction containing sIgA and oligonucleotides (ON). Gel-filtration of the AB fraction revealed the presence of ON with length 4-8 nucleotides co-isolating with sIgA. sIgA Preparations purified on DEAE-Fractogel and DNA-cellulose contained lipids which were phosphorylated in the presence of [gamma-32P]ATP. The affinity of HPLC-purified IgG and sIgA to calf thymus DNA, Escherichia coli DNA and total tRNA, and plasmid DNA was demonstrated. IgG was shown to bind to thymus DNA and E. coli DNA, and sIgA was shown to bind to E. coli DNA and tRNA. Nucleic acids of intestinal microflora are supposed to participate in induction of the secretory immune response.