Description: IgA comprises approximately 15% of all immunoglobulins. IgA in serum is mainly monomeric, but in secretions, such as saliva, tears, colostrums, mucus, sweat, gastric fluid, IgA is found as a dimer where they are connected by a joining peptide. Most IgA is present in secreted form. This is believed to be due to ist properties in preventing invading pathogens by attaching and penetrating epithelial surfaces. IgA is just a very weak complement activating antibody; hence it does not induce bacterial cell lysis via the complement system. However secretory IgA works together with lysozymes, also present in many secreted fluids, which hydrolyze carbohydrates in bacterial cell walls enabling the immune system to clear the infection. IgA which is predominantly found on epithelial cell surfaces where it acts as a neutralizing antibody.