IgA antibody is the first line of defense against infections at the mucous membrane. It is usually an early specific antibody. Which of the following statements regarding IgA is not true?

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 IgA1 by producing protease. It is the major immunoglobulin in milk, saliva, tears, and colostrum. IgA does not fix complement, so one would anticipate that a complement fixation test would not be useful for IgA antibody Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition