For this purpose, a transgenic mouse was developed (MBQ mouse) where macrophages exclusively expressed the MHC class II H2-Aq (Aq) on an H2-Ap (Ap) background. Aq, but not Ap expression mediates susceptibility to CIA through presentation of type II collagen (CII) to T cells. CIA severity is enhanced Nivolumab molecular weight by a mutation in

the Ncf1 gene, impairing reactive oxygen species (ROS) production by the phagocyte NADPH oxidase (NOX2) complex. Expression of functional Ncf1 on macrophages was previously shown to protect from severe CIA. To study the effect of ROS on macrophage-mediated priming of T cells, the Ncf1 mutation was introduced in the MBQ mouse. Upon CII immunization, Ncf1-mutated MBQ mice, but not Ncf1 wild-type MBQ mice nor Ncf1-mutated Ap mice, activated autoreactive T cells and developed CIA. These findings demonstrate for the first time that macrophages can initiate arthritis and that the process is negatively regulated by ROS produced via the NOX2 complex. Mice and rats with a lower capacity to produce reactive oxygen species (ROS) due to natural

polymorphisms in Ncf1 have an impaired capacity to exert oxidative burst in vivo 1 and develop more severe arthritis upon immunization 2, 3. Ncf1 gene encodes p47phox/Ncf1 that is a cytosolic regulatory component of the phagocyte NADPH oxidase (NOX2) complex. Using adoptive transfer experiments in the rat model it was shown that the protective effect of ROS on arthritis

development was mediated via T cells 3. This demonstrated that ROS production is buy Erlotinib an important regulator of T-cell activation, a finding that was confirmed in the mouse 2, 4. However, T cells themselves only produce minute amounts of ROS and no major differences in ROS production were observed between T cells from the different Ncf1 genotypes in mice or rats, indicating that in T cells ROS production was independent of the NOX2 complex 5. This observation led to the hypothesis that APC produce ROS into the immunological synapse, oxidize the T-cell surface and thereby downregulate T-cell activation 5. Although MHC class II expressing macrophages (here defined in its broadest sense, i.e. including monocytes) and B cells can also present antigens, DC are considered to be the only APC that can prime naïve T cells and L-gulonolactone oxidase initiate immune responses 6. However, DC and B cells are rather inefficient in producing ROS, whereas macrophages are much more potent 7. This led us to investigate the role of ROS produced by macrophages in T-cell activation in a mouse model for arthritis. In a transgenic mouse model where only macrophages expressed functional Ncf1 on an Ncf1-deficient background, the mice were protected from development of severe arthritis 7, indicating that in fully mutated mice the absence of macrophage derived ROS was partially mediating the severe arthritis.