The DNA fragment coding the full-length H2-DMb2 [30] was amplified by PCR with two primers (59-ATGGCTGCACT-CTGGCTGCTGCTGCTGGT-39 and 59-GATGCCGTCCT- TCTGGGTAGGTGGATCC-39). The PCR product was cloned into the CMV promoter-driven expression plasmid pDsRedN1 (BD Clontech). This construct omitted the stop codon of H2-DMb2 and encoded the H2-DMb2 fused with DsRed. The cloned plasmid DNA was transfected to macrophage hybridoma clone 39 with Effectene transfection reagent (Qiagen) according to the manufacturer's protocol. During the transfection to clone 39, the medium containing cDNA and the transfection reagent was replaced with fresh medium after an 8-h transfection, and then clone 39 was cultured for 40 h. To obtain stable cell lines, clone 39 was passaged at 1:5 into RPMI 1640 containing 10% FCS with 50 mg/ml geneticin (G-418; Sigma-Aldrich). Cells showing the best fluorescence were selected using a FACS Vantage cell sorter (BD Bioscience). After cell sorting, clone 39 expressing DM-DsRed was cultured in RPMI 1640 containing 10% FCS with 200 mg/ml geneticin.