How many sites on this antibody molecule have potential to bind to a non-self molecule?

There are two sites on the antibody molecule that have a potential to bind to a non-self molecule. The Fab of an antibody is the region of the antibody that binds to an antigen. It consist of one constant and one variable domain from each heavy and light chain of the antibody. During immune reaction, an antigen-antibody reaction occurs between the antibodies made by the B cells and the antigens.