Colostral mononuclear phagocytes are able to kill enteropathogenic Escherichia coli opsonized with colostral IgA

Enteropathogenic Escherichia coli (EPEC) is the main aetiological agent of acute diarrhoea among low socioeconomic level infants in developing countries. Breast-feeding provides infant protection against acute gastrointestinal and respiratory infections; however, little is known about the protective role of colostral phagocytes in the gut of newborn infants. In the present investigation we studied the ability of human colostral MN phagocytes to kill EPEC as well as the interactions between these cells and colostral and serum opsonins. The authors observed that the microbicidal activity of colostrum MN phagocytes was dependent on previous EPEC opsonization with colostral supernatant or blood serum. A defatted colostrum supernatant pool presented opsonic activity for EPEC killing at levels equivalent to those of normal serum. IgA-depleted colostrum supernatant showed significantly lower opsonic activity, whereas purified IgA from the same colostrum pool was a potent opsonin which induced EPEC killing at levels equivalent to those of untreated colostrum. Colostral MN phagocytes are able to release superoxide anion when incubated with both EPEC opsonized with untreated colostrum and purified IgA. Purified IgA was also able to restore opsonic activity of IgA-depleted colostrum. A colostrum pool without C3 and IgG induced EPEC killing by colostral MN phagocytes at rates equivalent to those of untreated colostrum supernatant. Addition of an IgM MoAb (My43) anti-human Fc alpha receptor resulted in a significant inhibition of EPEC killing when bacteria were opsonized with purified IgA, suggesting an interaction between IgA and Fc alpha R. With respect to serum opsonins, we observed that IgG plus complement component C3 were necessary to induce EPEC killing by the colostrum MN phagocytes. Colostral phagocyte killing of enteropathogenic bacteria may represent an additional mechanism of breast-feeding protein against intestinal infections during the first week of life.