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 bacteria. It is also a major immunological defence mechanism, detecting natural commensals and triggering immune response when toxic microbes are present. Failure of homeostasis due to trauma, drugs and infectious microbes not only damages the gut but can lead to influx of damaging agents into the bloodstream. These mechanisms have relevance for multiple conditions affecting all areas of the world and socioeconomic groups such as ulcers, inflammation, and infectious diarrhoea. There is currently much interest in the potential value of colostrum for the prevention and treatment of these conditions as it is derived from natural sources and can influence damaging