An organism or infectious agent that causes disease is called a(n) . a molecule that can elicit an immune response is called a(n) . proteins that directly attack foreign antigens are . protection against infection requires the ability to recognize substances as nonself. many of the proteins on the surfaces of our cells are encoded by genes that belong to the major complex. a cell that displays a foreign antigen is called an antigen- cell. the human antigens are linked to sugars and form branchlike glycoproteins.