Increased antigenicity of a membrane-bound polypeptide produced from a plant is provided in a process in which extraction of the polypeptide or other compounds from the plant is such that phospholipids are associated with the polypeptide. Reducing fat by supercritical fluid extraction increases antigenicity of such plant-produced membrane-bound polypeptides. Methods and means of producing such membrane-bound polypeptides are provided. Methods to produce a protective response in animals are provided by administering to the animal the membrane-bound polypeptide. Binding of antibody specific to the membrane-bound polypeptide is increased. The process provides for increased preferred formation of the membrane-bound polypeptide. Stability of the membrane-bound polypeptide is increased when the plant material is defatted.
