Secretory immunoglobulin A obtained from pooled human colostrum and milk for oral passive immunization

Passive immunization is useful in cases of immunodeficiencies or infectious diseases, but usually seric gammaglobulin or hyperimmune sera are administered parenterally, providing good systemic immunization, though with low protection of the mucosal surfaces. The oral administration of secretory antibodies, especially surface immunoglobulin (SIg)A, which is perfectly adapted to the mucosal environment, would therefore, be preferable. The aim of the present study was to obtain a SIgA preparation from pooled human colostrum and milk, which should maintain the essential properties of the antibodies suitable for clinical oral administration. IgA preparations were obtained from colostrum and milk pools by salt precipitation. The final products were evaluated in terms of yield and purity, as well as antibody activity to bacterial antigens and toxins and inhibitory activity of bacterial adhesion to epithelial cells. The best yield and purity were achieved when the colostrum pool was used as a source of IgA; the final product showed very few bands of protein contamination. The IgA preparations preserved the antibody reactivity against various microbial antigens, well comparable with the reactivity exhibited by the original milk and colostrum pools. SIgA preparations were able to inhibit greatly the adhesion of enteropathogenic Escherichia coli to Hep-2 cells and the invasion of enteroinvasive E. coli. These promising results show the feasibility of obtaining SIgA suitable for oral use, which may in future be administered to immunodeficient patients with gastrointestinal manifestations, from human colostrum and milk.