Which antibody has the maximum concentration in GI Secretions -

Ans. is 'c' i.e., IgA IgA antibody o It is the second most abundant antibody (after IgG). o It is major immunoglobulin in colostrum, saliva, tears, respiratory and gastrointestinal secretions. o IgA occurs in two forms. IgA | | | Serum IgA Secretory IgA (SIgA) o Monomer o Found in serum o Dimer o Two monomer units are joined together by a glycopeptide - J chain o Contains glycine-rich polypeptide secretory component, which protects IgA from denaturation by bacterial proteases. o SIg A and J chain are synthesized by plasma cells, o Secretory component is produced by mucosal or glandular epithelial cells. o Two subclasses of IgA have been described IgA1 & IgA2 # Ig Al - Predominant serum IgA # Ig A2 - Predominant secretory IgA