Ruxolitinib (Ruxo) reduces the expansion of T cells and neutrophils in secondary HLH. (A) Frequency (upper panels) and absolute numbers (lower panels) of splenic CD8⁺ T cells (left panels) and CD4⁺ T cells (right panels) gated on CD19⁻TCRβ⁺ cells. (B) Representative flow cytometric plots showing Ly6C^hiLy6G⁻ monocytes and Ly6G⁺Ly6C^int neutrophils gated on CD19⁻TCRβ⁻NK1.1⁻CD11c⁻CD11b⁺ cells. Summarized data are the frequency (upper right panels) and absolute numbers (lower right panels) of splenic monocytes and neutrophils. Each data point represents 1 mouse, and data were collected from 3 independent experiments. The mean ± standard deviation are shown. (C) Representative images showing hematoxylin and eosin–stained sections of liver (top row) and immunohistochemical-stained sections of liver showing CD3⁺ (middle row) and Neut7-4⁺ (bottom row) cells from mice injected with PBS (Naive) or CpG and αIL-10R that were left untreated (UnRx) or treated with αIFN-γ or Ruxo. Original magnification ×200. The total number of mice per group was n = 12 each (Naive and UnRx), n = 14 (IFN-γ) and n = 13 (Ruxo). (D) Summarized data from liver histological analyses showing the area of tissue infiltrated by immune cells (upper left panel), the number of inflammatory foci per field of view at 2× magnification (upper right panel) and the percentages of CD3⁺ cells (lower left panel) and Neut7-4⁺ cells (lower right panel) within inflammatory foci. 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.