Human IgA occurs in multiple molecular forms (polymeric and monomeric) and two subclasses which show differential distribution between the mucosal and circulatory compartments of the immune system. In humans, 85–90% of IgA antibodies are found in body secretions such us saliva, tears, breast milk; gastrointestinal mucous membranes, urogenital and respiratory tracts and prostatic fluid, among others. The other 10-15% of IgA antibodies are found in blood as monomeric, IgA1, and polymeric forms IgA2. IgA1 is present 5 times more than IgA2.