All colostrum and milk will contain some sIgA, even those collected from cattle. The sIgA present in these secretions may contribute to the protective effects of immune milk products. Secretory IgA is considered to be the primary immunoglobulin responsible for immune protection of mucosal surfaces such as the intestine [158] . Secretory IgA and sIgM, as polymeric forms of the respective immunoglobulins, are stabilized by their binding to SC. They have antimicrobial properties such as agglutination of microbes and neutralization of viruses, and noninflammatory extracellular and intracellular immune exclusion by inhibiting adherence and invasion of mucosal epithelia [158] . The intracellular immune exclusion occurs when sIgA is being transcytosed by the enterocytes and comes into contact with viral particles within the endosomic system [15] . Secretory IgA also neutralizes pathogens in the intestinal lumen [173] . Bacterial enterotoxins may be neutralized by binding sIgA and internalization into intestinal epithelial cells [174] .