Ruxolitinib (Ruxo) reduces the expansion of T cells and neutrophils in primary HLH. (A) Summarized data of the frequency and absolute numbers of splenic CD8⁺ T cells (left panels), CD4⁺ T cells gated on TCRb⁺CD19⁻ live cells (middle panels), and LCMV-specific (Db gp33) CD8⁺ T cells gated on CD8⁺ T cells (right panels). (B) Frequency of splenic monocytes (Ly6C^hiLy6G⁻) and neutrophils (Ly6C^intLy6G⁺) of CD11b⁺CD11c⁻ cells. Data (mean ± standard deviation) are representative of 2 independent experiments. n = 5 mice per group. (C) Representative hematoxylin and eosin–stained liver sections (top row) and immunohistochemical staining of CD3⁺ (middle row) and Neut7-4⁺ (lower row) cells from naive Prf1^−/− mice or mice infected with LCMV that were left untreated (UnRx) or treated with αIFN-γ or Ruxo. Original magnification ×200. (D) Data were quantitated and plotted as percentage area of inflammation (upper left panel), number of inflammatory foci per field of view at 2× magnification (upper right panel) and the percentages of Neut7-4⁺ cells (lower left panel) and CD3⁺ cells (lower right panel). Data were collected from 2 independent experiments (n = 4 mice per group). Samples were randomly chosen for histological analysis. *P < .05, **P < .01, ***P < .001, ****P < .0001.