Increased antigenicity of a membrane bound polypeptide produced from plants is provided by reducing fat content of the plant, plant part, or plant tissue producing the polypeptide. Methods and means of producing such plant material are provided. Methods to produce a protective immune response in animals are provided by administering to the animal the plant, plant part of plant tissue which has reduced fat content and which comprises the polypeptide or by administering to the animal an extracted polypeptide produced from such a plant.
