Total RNA was extracted from hybridoma cells using the TRIzol reagent (Invitrogen) and mRNA was isolated with the NucleoTrap mRNA Mini Kit (Macherey-Nagel GmbH & Co. KG.). Purified mRNA was reverse transcribed using oligo (dT) as a primer in a ThermoScript RT-PCR system (Invitrogen). The variable heavy-and light-chain domains (V H and V L ) were amplified from the cDNA product by PCR with a variety of primer sets [35, 36] . The PCR products were cloned using the TA kit (Promega) and the V H and V L sequences were determined by DNA sequencing. Software Vector NTI was used for sequence analysis. From these sequences, the framework regions (FRs) and complementarity-determining regions (CDRs) were analyzed by comparing them with those found in the Kabat database and the ImMunoGeneTics database [37] .