Before revision:  An instance of this problem is immune discrimination between self and not-self . We connect this problem to biochemical adaptation , and establish thatligand antagonism - the ability of sub threshold ligands to negatively impact response - is a necessary consequence of absolute discrimination .
After revision:  An instance of this problem is immune discrimination between self and not-self , where it is also observed experimentally that ligands just below discrimination threshold negatively impact response, a phenomenon called antagonism. We characterize mathematically the generic properties of such discrimination, first relating it to biochemical adaptation , and establish thatligand antagonism - the ability of sub threshold ligands to negatively impact response - is a necessary consequence of absolute discrimination .