(A) Kinetic profile of the hydrolyzed and cyclized haptens of piperacillin bound to each modified lysine residue on albumin in cell culture. Profiles derive from MRM-MS analysis of the modified tryptic peptides. (B) Proliferative response of PBMC from hypersensitive patients pulsed with piperacillin for 1-96 h. Proliferative responses were analyzed by incorporation of [3H]thymidine of the final 16 h of the experiment. (C) Model of albumin showing piperacillin binding sites at positions Lys190, Lys195, Lys199, Lys212, Lys351, Lys432, Lys525 and Lys541.