P166 Associating IFN gamma production to clinical and laboratory features of CPG-induced macrophage activating syndrome (MAS) in mice
Introduction Repeated TLR9 stimulation was recently found to result in a macrophage activation syndrome (MAS)-like disease in mice [1] . Mice administered CpG (TLR9-ligand) developed cytopenia, anemia, thrombocytopenia, splenomegaly, hepatitis, and hyperferritemia. Administration of the anti-mouse IFNg monoclonal antibody (mAb), XMG1.2, was found to ameliorate disease. Our aim was to extend these studies by performing a comprehensive biomarker study to correlate the kinetics of IFNg production to disease endpoints. Methods Mice were administered CpG on days 0, 2, 4, 7 and 9. Tissue and blood were obtained at numerous time-points. Gene analysis and histology were performed on spleen and liver. Serum cytokines were analysed using the multiplex Luminex technology and leukocyte, red blood cell and haemoglobin counts were assessed using a haematological counter. Results Our results confirmed a multi-phasic production of IFNg in serum, spleen and liver following injection of CpG. The initial peak of IFNg production correlated with a rapid appearance of cytopenia and thrombocytopenia followed by the other features of MAS (e.g., anemia and splenomegaly). Gene analysis confirmed the induction of IFNg-related signature molecules in the spleen and liver. Conclusion In mice, repeated CpG injection leads to a MAS-like disease that is manifested by a multi-phasic production of IFNg. Disease parameters including anemia, decreased hemoglobin, splenomegaly, hypercytokinemia and ferritinemia were consistent with IFNg production. Finally, IFNg-induced biomarkers were also established in tissues from MAS-mice (e.g. CXCL10 and Class II major histocompatibility complex transactivator (CIITA)). The use of XMG1.2 will be used in the aim to correlate disease biomarkers and IFNg production at different time-points of disease progression. Our study, thus, allows us to more fully understand the physiologically-based pharmacokinetic (PK)/pharmacodynamics (PD) relationships based on IFNg -neutralization in the murine model of MAS.