Abstract: The invention provides compositions and methods for specific binding to a region of the polymeric immunoglobulin receptor (pIgR) of a cell with the provisos that the ligand does not substantially bind to the most abundant form of the secretory component (SC) of pIgR present in an organ of interest of an animal of interest under physiological conditions, and does not bind to the pIgR stalk. In some embodiments, the ligand decreases cleavage of SC from the stalk by at least one-third. The ligands and methods of the invention can be used with both birds and mammals. In more preferred embodiments, the animal is a mammal. In the most preferred embodiment, the animal is a human. The ligand may be targeted into the cell or may undergo retrograde transcytosis and release at the basolateral side of the cell, and may comprise a biologically active composition.

Abstract: The immunoglobulins of the present invention are useful therapeutic immunoglobulins against mucosal pathogens such as S. mutans. The immunoglobulins contain a protection protein that protects the immunoglobulins in the mucosal environment. The invention also includes the greatly improved method of producing immunoglobulins in plants by producing the protection protein in the same cell as the other components of the immunoglobulins. The components of the immunoglobulin are assembled at a much improved efficiency. The method of the invention allows the assembly and high efficiency production of such complex molecules. The invention also contemplates the production of immunoglobulins containing protection proteins in a variety of cells, including plant cells, that can be selected for useful additional properties. The use of immunoglobulins containing protection proteins as therapeutic antibodies against mucosal and other pathogens is also contemplated.