Which of the following statements regarding IgA is true?
|A||Complement fixation test for IgA antibody will be positive if specific IgA antibody is present.|
|B||IgA can be destroyed by bacterial proteases|
|C||IgA is absent in colostrum|
|D||IgA is not found in saliva; therefore an IgA diagnostic test on saliva would have no value.|
Each secretory IgA molecule has a molecular weight of 400,000 and consists of two H2L2 units and one molecule each of J chain and secretory component. Some IgA exists in serum as a monomer H2L2 with a molecular weight of 160,000. Some bacteria, such as Neisseria, can destroy IgA-1 by producing protease. It is the major immunoglobulin in milk, saliva, tears, mucus, sweat, gastric fluid, and colostrum. IgA does not fix complement, so one would anticipate that a complement fixation test would not be useful for IgA antibody.