Functional inhibition of iTreg by monoclonal antibodies against cell surface molecules. PBL of 9 healthy control individuals were separated from heparinized whole blood and incubated for 16 h with medium or PMA/Ionomycin. Then, CD4+CD25+CD127-IFNγ+ PBL were separated from CD4+CD25+CD127-IFNγ- PBL and both cell fractions were added to autologous PBL that were stimulated with PMA/Ionomycin for another 3 days in the absence or presence of monoclonal antibodies against cell surface molecules of iTreg such as CD178, CD152, CD279, CD28, CD95, and HLA-DR. Cell proliferation was measured as counts per minute (cpm) of 3 H-thymidine incorporation. All co-cultures with separated CD4+CD25+CD127-IFNγ+ PBL showed lower cell proliferation than co-cultures with separated CD4+CD25+CD127-IFNγ- PBL (p < 0.05). Addition of monoclonal antibodies against CD28, CD152 and CD279 increased cell proliferation in cell cultures containing CD4+CD25+CD127-IFNγ- PBL (p < 0.05). Of cell cultures with CD4+CD25+CD127-IFNγ+ PBL, only those with CD28 monoclonal antibody showed a slightly increased cell proliferation (p < 0.05). Data are given as mean±SD. *p < 0.05.