Combining this information raised the question whether macrophages can also prime naïve T cells and whether this capacity is influenced by ROS. Until now there are no clear reports that macrophages can activate naïve

CD4+ T cells and initiate an immune response. We have previously shown that ROS secretion by APC oxidizes T-cell membrane proteins and thereby downregulates Alvelestat T-cell activation 5. To investigate the effect of ROS deficiency on macrophages in an arthritis model we developed a transgenic mouse in which only CD68 expressing (CD68+) cells (commonly defining and in text referred to as macrophages 8) can present type II collagen (CII), the antigen used for immunization. The capacity to process and present CII peptides is associated with the expression click here of the MHC class II H2-Aq molecule (Aq): Aq expressing APC efficiently activate specific T-cell hybridomas by presenting CII, whereas Ap expressing APC present the same CII peptides but are less efficient in processing

the CII protein, resulting in only very low levels of CII specific T-cell hybridoma activation 9. In a similar fashion, arthritis susceptibility is dependent on MHC II: the Aq haplotype confers susceptibility to CIA, while the Ap haplotype confers a relative resistance 10, 11. The transgenic mice used in this study expressed Aq under control of the hCD68 promoter on the Ap background. The Ncf1 mutation as described above was introduced on this background. In these mice we were able to show that in a

ROS deficient environment Aq expressing macrophages were able to prime naïve T cells and induce CIA development. These data indicate a novel role for macrophages in initiating immune responses and suggest that in situations with lower ROS production (auto) immunity may develop as a result of increased T-cell activation. The MHC II haplotype determines the susceptibility to CIA in mice: on the C57/Bl10 background, two congenic strains for the MHC locus, B10.Q (Aq) and B10.P (Ap), differ in arthritis susceptibility 10. B10.Q mice are susceptible while B10.P mice are resistant to CIA 10. We first investigated if Ncf1 mutated mice that develop severe Cyclooxygenase (COX) arthritis on the B10.Q background 2, also developed arthritis on a B10.P background. We confirmed that Ncf1 mutated mice that express Aq (B10.Q.Ncf1*/*) develop severe disease with high incidence 2, but Ncf1-mutated mice homozygous for Ap hardly develop arthritis (Figs. 1A and B). At least one allele of Aq was required for arthritis development. Anti-CII IgG levels were measured in sera taken at day 42 or when the mice were sacrificed at day 82. Levels of anti-CII IgG were highest in the B10.Q.Ncf1*/* mice and decreased with increasing number of Ap alleles; thus following the disease severity. Mice homozygous for Ap had very low levels of anti-CII IgG suggesting a lack of efficient T-cell help to B cells (Fig. 1C).