In this study we specifically sought to determine whether Treg cells impact on acute innate immune responses in vivo. For this purpose, we used a mouse model of melanoma. Mouse melanoma cells (B16F10), and particularly those engineered to express Fas ligand (B16FasL), induce an innate immune response following their subcutaneous inoculation into C57BL/6 (B6) mice.8 This innate immune response is important

because it clearly contributes to tumour rejection. We have previously reported that an in vivo reduction in Treg-cell numbers promotes rejection of both B16 and B16FasL and that this is at least partly the result of enhanced inflammatory responses in these animals compared with those with an intact Treg-cell population.9 As B16FasL induces a

more readily detectable and measurable inflammatory response compared with B16, this model provided an opportunity to address whether Treg cells limit acute innate RG7420 concentration immune responses in the skin, a site where at least one-fifth of skin-resident CD4+ IWR-1 T cells are Treg cells. The C57BL/6 (B6) mice were bred and maintained at Biomedical Services (Cardiff, UK). All experiments were performed in compliance with UK Home Office regulations. Hybridomas secreting CD25 (PC61, rat IgG1), Escherichia coliβ-galactosidase- (GL113, rat IgG1, non-depleting isotype control antibody), Gr-1- (RB6-8C5, rat IgG2b) specific monoclonal antibodies (mAbs) have been described previously.8,10,11 Briefly, 0·5 mg PC61 or GL113 was administered intraperitoneally (i.p.) 1 and 3 days before tumour inoculation. As we have previously shown, PC61 administration in this way efficiently depletes

the majority of CD25+ cells.9,11,12 However, it is also clear that many Foxp3+ Treg cells (20–50%) do not express CD25 and therefore escape the depleting effect of PC61 administration.13 Administration of PC61 therefore results in a reduction Resveratrol rather than a complete loss of Treg-cell activity. Neutrophils were depleted by administration of 0·3 mg of RB6-8C5 every second day from 1 day before tumour inoculation. The efficiency with which RB6-8C5 depletes neutrophils has been described elsewhere.9 B16F10 (B16) and B16F10 transfected with the Fas ligand B16FasL were generated as previously described 14 and were maintained in R10, which consists of RPMI-1640 medium (Gibco – Invitrogen, Carlsbad, CA) supplemented with 10% fetal calf serum (Gibco – Invitrogen), penicillin–streptomycin, l-glutamine, non-essential amino-acids (Life Technologies – Invitrogen, Carlsbad, CA) and 50 μm 2β-mercaptoethanol (Sigma-Aldrich, St Louis, MO). In the case of B16FasL, G418 was added to the media at a final concentration of 1·5 mg/ml to maintain expression of FasL. Tumour cells were either injected subcutaneously (s.c.) (105 in 100 μl phosphate-buffered saline) or i.p. (2 × 106 in 100 μl PBS). Tissue was taken from the area surrounding the inoculation site and fixed in zinc fixative as previously described.