LacZ-inducible T cell hybridomas specific for NP 366 peptide [37, 54] were resuspended at 1610 6 cell/mL and aliquots (100ml) and dispensed into 96-well flat-bottom plates together with 5610 5 naïve splenocytes (APCs). Cells were cultured in the presence of NP 366 or NPN3A peptides at concentrations ranging from 10 215 M to 10 24 M for 18h at 37 0 C. The cells were then washed with PBS, fixed with 100ml of 2% formaldehyde/0.2% glutaraldehyde in PBS for 5min on ice, washed in PBS and incubated with 2.5mg of 5-bromo-4-chloro-3-indolyl b-D-galactoside (X-gal) for 16h at 37 0 C. The LacZ + hybridomas were then counted using a light microscope, and the number of NP 366 -specific hybridomas was calculated by subtracting the ''background'' LacZ expression for cells cultured in the absence of the peptide.