Immunoglobulin A only weakly. IgA exists in two isotypes, IgA1 and IgA2. They are both heavily glycosylated proteins. While IgA1 predominates in serum (~80%), IgA2 percentages are higher in secretions than in serum (~35% in secretions); the ratio of IgA1 and IgA2 secreting cells varies in the different lymphoid tissues of the human body: Both IgA1 and IgA2 have been found in external secretions like colostrum, maternal milk, tears and saliva, where IgA2 is more prominent than in the blood. Polysaccharide antigens tend to induce more IgA2 than protein antigens. Both IgA1 and IgA2 can be in membrane-bound form. ("see B-cell receptor")
Colostrum on adult gut health in several recent well controlled published studies. Evidence for the beneficial effect of colostrum on extra-gastrointestinal problems is less well developed, due in part to the limited number of randomised double-blind studies published, although a variety of possible uses have been suggested. Dairy cattle are naturally exposed to pathogens and produce immunoglobulins against them. These antibodies are present in the cow’s bloodstream and in the colostrum. These immunoglobulins are specific to many human pathogens, including "Escherichia coli, Cryptosporidium parvum, Shigella flexneri, Salmonella "species", Staphylococcus" species, and rotavirus (which causes diarrhea in infants). Before the development of