Human immunoglobulin A can be described by which of the following statements?

Immunoglobulin A is the predominant immunoglobulin in body secretions (IgG is predominant in serum). Each secretory IgA molecule is a dimer consisting of a secretory component and a J chain. The secretory component, a protein of molecular weight 70,000, is synthesized by epithelial cells and facilitates IgA transpo across mucosal tissues. The J chain is a small glycopeptide that aids the polymerization of immunoglobulins. IgA exists as two subclasses: IgAI (75% of the total) and IgA2 (25% but more prevalent in secretions). IgA provides defense against local infections in the respiratory, gastrointestinal, and genitourinary tracts, and prevents access of foreign substances to the general systemic immune system. It also can prevent virus binding to epithelial cells. IgM, not IgA, is the principal immunoglobulin in the primary immune response and is the usual antibody in cold agglutinins. The half-life of IgA is about 6 days; IgE has the shoest half-life, approximately 2 to 2.5 days. Ref : Ananthanarayana textbook of Microbiology 9th edition Pgno : 97