In the current study, we sought to determine the role of CXCL9 in pathogenesis in murine models of both Familial HLH (prf1−/−) and Toll Like Receptor (TLR) 9 repeated stimulation induced Macrophage Activation Syndrome (MAS), a form of secondary HLH. Here, CXCL9 is linked to macrophage activation syndrome.