The serine protease CatG uniquely was able to cleave MHC II molecules in vitro. CatG is abundant in storage granules of neutrophils; it is released in inflammatory sites and contributes to innate

protection from bacterial infection. Non-immune roles for CatG are suggested by subtle developmental defects in CatG-deficient mice.18 Notably, CatG is expressed in primary human APCs, such as B cells, monocytes, and myeloid and plasmacytoid DCs,19,20 where it has been shown to contribute to proteolytic antigen processing.21 Here, we characterized the specificity of CatG cleavage of MHC II molecules in vitro, and examined whether CatG contributes to MHC II turnover in vivo. The HLA-DM-deficient human B-LCLs 9.5.3 and 5.2.4, their parent line 8.1.6 and the 5.2.4-DR3 transfectant have been described previously.22–24 Transduced find protocol B-LCL 5.2.4 expressing the mutant HLA-DR3 molecules

DRB R74Q, DRB D152N, DRB S197N and DRB E187K have been described.24,25 Schneider-2 Drosophila melanogaster (S2) cells expressing recombinant soluble HLA-DR molecules have been described previously.26,27 Mammalian cells were cultured in complete RPMI-1640 medium supplemented with 10% fetal bovine serum (FBS) (HyClone Laboratories, Logan, UT) and 2 mm l-glutamine (Life Technologies, Carlsbad, CA). S2 cells were cultured as described previously.28 Human peripheral blood mononuclear cells (PBMC) were isolated from buffy coats of healthy donor blood. B cells and myeloid type 1 dendritic cells (mDC1s) were positively selected using immunomagnetic selleck chemicals beads specific for CD19 and CD1c, respectively [magnetic-activated cell sorting (MACS); Miltenyi Biotec, Auburn, CA] according to the manufacturer’s protocols. The purity of primary cell preparations routinely exceeded 90%. Cells were cultured in the presence or absence

of the CatG-specific inhibitor I (10 μm; Calbiochem, San Diego, CA; Compound 7 in29) or E64d (10 μm; Calbiochem) for 4·5, 24 or 72 hr at 37°, and either analysed by flow cytometry or prepared for western blotting by lysis in 10 mm Tris (pH 7·5), 150 mm NaCl, 0·5% NP-40, and CatG-specific inhibitor (1 μm), Janus kinase (JAK) followed by adjustment for equal total protein content (quantified by the Bradford assay). Purification of full-length native HLA-DR molecules was performed essentially as described previously.26,27 Briefly, B-LCLs were lysed in 10 mm Tris (pH 7·8), 140 mm NaCl, and 0·5% NP-40. The lysate was pre-cleared by centrifugation and filtration and passed over an anti-DR (L243)-sepharose immunoaffinity column (L243: IgG2a anti-DR). The column was washed extensively (50 mm Na-phosphate, 150 mm NaCl and 1% octylglucoside, pH 8) and eluted at high pH (100 mm glycine-NaOH and 1% octylglucoside, pH 11). Soluble HLA-DR was purified from insect cell supernatants by a similar method, except that detergents were omitted.