Patent No. 583894 Disclosed is a peptide consisting of a sequence within the sequence KTTNVSLYPGYNFRYAKYYKENNVEKRTLIKVFGIRFDILVFGTGGKFD or consisting of the sequence KTTNVSLYPGYNFRYAKYYKENNVEKRTLIKVFGIRFDILVFGTGGKFD, said peptide being useful as an immunogen to generate an antibody that binds to a non ATP-binding P2X7 receptor but not to an ATP-binding P2X7 receptor.