Secretory IgA antibodies against cow's milk proteins in human milk and their possible effect in mixed feeding.

Antibodies of the secretory IgA type against cow's milk proteins were consistently found in human milk. With the assumption that such antibodies can help to prevent or at least diminish the contact between native cow's milk proteins and the lymphoid system of babies on mixed feeding, the levels of antibodies of various immunoglobulin classes against bovine milk proteins were measured in different groups of babies. Those on artificial feeds who had been on mixed feeding of human milk and cow's milk for less than 1 week had significantly higher levels of IgG antibodies to cow's milk proteins than those who had been on mixed feeding for a period longer than 3 weeks.