[Immunochemical properties of secretory IgA of human colostrum]

Immunochemical properties of secretory IgA obtained from the colostrum of healthy post-partum women are discussed. Lipids were completely eliminated by centrifugation and the supernatant was adjusted at pH 8.0 with NaOH and dialysed against a PBS buffer. Fractionation through a Sephadex G-200 column was fractionated again through a DEAE-cellulose column which eluted only pure IgA. Aliquots of 3 ml each were checked for protein content in an Uvicord spectrophotometer at 254 millimicron. Three fractions were obtained from the Sephadex column, the first involving tubes 50 to 90 contained IgA and IgM, the second from tubes 91 to 120 contained IgG and the third from tubes 130 to 150 contained alfa-lactalbumin and lactotransferrin. Passage of fraction I through a DEAE-cellulose column led to the collection of pure IgA in tubes 45 to 80 with the highest content in tube 53 which was employed in the immunization of rabbits. Ouchterlony immunodiffusion and immunoelectrophoresis were employed to check the reactivity among whole colostrum as well as Sephadex and DEAE-cellulose fractions against an anti-IgA, anti-IgM, anti-IgG, anti-immunoglobulins and anti-whole human sera. Several precipitin bands revealed that human colostrum contained IgA, IgG, and IgM. Pure secretory IgA was used to immunize adult rabbits with complete and incomplete Freund's adjuvant for a period of two months. A rabbit anti-IgA serum was then obtained and after being purified by saline precipitation and dialysis and passed through a DEAE-cellulose column, was labeled with I-131 reaching a specific activity of 20 microCi/mg. This antiserum was used against human colostrum, normal serum and saliva, and serum and urine from a patient with an IgA myeloma confirmed by means of precipitin methods and autoradiographies. Chemical purity of the secretory IgA was confirmed by analytic ultracentrifugation obtaining a sedimentation value of S 20: 10.5. In all cases a single precipitin band was obtained in spite of the low concentration of the antigens; the isotopic labelling did not alter the specificity and the sensitivity of the antiserum and its usefulness was well established. The biological properties of secretory IgA are described and its importance in local immunity is emphasized.