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.