The secretory component of immunoglobulin molecule is -

The secretory component is a component of immunoglobulin A (IgA). Secretory component is a proteolytic cleavage product of the polymeric immunoglobulin receptor which remains associated with dimeric IgA in sero-mucus secretions. Polymeric IgA binds to the polymeric immunoglobulin receptor on the basolateral surface of epithelial cells and is taken up into the cell transcytosis. Ref: Ananthanarayan & Panikers textbook of microbiology 9th edition pg:97