Figure 3.
Cell surface–bound IFNγ mediates persistent JAK/STAT signaling even after cytokine washout. (A) Human macrophages were stimulated with IFNγ (100 ng/ml) for 8 h, washed, and then cultured in regular media or media containing ruxolitinib (1 µM) or increasing concentrations of anti-IFNγ neutralizing antibody for an additional 28 h. Cells were collected, and whole cell western blotting for phosphorylated STAT1 and IRF1 was performed at indicated time points. Representative blot of duplicates from two separate subjects. (B) Human macrophages were stimulated with 100 ng/ml IFNγ for 3 h, washed, and then cultured in either ruxolitinib (1 µM), anti-IFNγ neutralizing antibody (10 µg/ml), or isotype control antibody (10 µg/ml) for 2 h. Samples were collected at the indicated times for immunoblot. Representative blot of duplicates from two separate subjects. (C) Quantification of pSTAT1 band intensities from B. (D) Human macrophages were stimulated with 100 ng/ml IFNγ for 8 h, washed, and cultured for an additional 88 h in regular media. Supernatants from stimulated macrophages were collected after the 8-h stimulation and 88 h after washout. This supernatant was used to stimulate fresh macrophages for 1 h in the presence/absence of ruxolitinib (1 µM) or anti-IFNγ neutralizing antibody (10 µg/ml). As a control, fresh macrophages were stimulated with media supplemented with 1 ng/ml IFNγ for 1 h. Representative blot of duplicates from two separate subjects. (E) Macrophages were left in regular media or pre-treated with 10 µg/ml CHX for 15 min and stimulated with 100 ng/ml IFNγ for 3 h. Treated macrophages were washed and subsequently cultured for 2 h in regular media, media supplemented with 10 µg/ml CHX, or anti-IFNγ neutralizing antibody (10 µg/ml) and collected for immunoblot. Duplicates from one subject are shown. (F) Quantification of pSTAT1 band intensities in E normalized to band intensity of macrophages treated with IFNγ for 3 h. (G) Human macrophages were stimulated with 100 ng/ml IFNγ for 8 h, washed, and cultured in regular media or media supplemented with 1 µM ruxolitinib for 16 h. After 16 h, cells were washed again and cultured in regular media for an additional 24 h. Cells were collected for immunoblot at indicated times. Representative blot of four replicates from two subjects. (H) Quantification of pSTAT1 band intensities in G normalized to band intensity of macrophages treated with IFNγ for 3 h. Statistical tests were determined by a single-tailed t test. *P < 0.05, **P < 0.01, and ***P < 0.001. Source data are available for this figure: SourceData F3.

Cell surface–bound IFNγ mediates persistent JAK/STAT signaling even after cytokine washout. (A) Human macrophages were stimulated with IFNγ (100 ng/ml) for 8 h, washed, and then cultured in regular media or media containing ruxolitinib (1 µM) or increasing concentrations of anti-IFNγ neutralizing antibody for an additional 28 h. Cells were collected, and whole cell western blotting for phosphorylated STAT1 and IRF1 was performed at indicated time points. Representative blot of duplicates from two separate subjects. (B) Human macrophages were stimulated with 100 ng/ml IFNγ for 3 h, washed, and then cultured in either ruxolitinib (1 µM), anti-IFNγ neutralizing antibody (10 µg/ml), or isotype control antibody (10 µg/ml) for 2 h. Samples were collected at the indicated times for immunoblot. Representative blot of duplicates from two separate subjects. (C) Quantification of pSTAT1 band intensities from B. (D) Human macrophages were stimulated with 100 ng/ml IFNγ for 8 h, washed, and cultured for an additional 88 h in regular media. Supernatants from stimulated macrophages were collected after the 8-h stimulation and 88 h after washout. This supernatant was used to stimulate fresh macrophages for 1 h in the presence/absence of ruxolitinib (1 µM) or anti-IFNγ neutralizing antibody (10 µg/ml). As a control, fresh macrophages were stimulated with media supplemented with 1 ng/ml IFNγ for 1 h. Representative blot of duplicates from two separate subjects. (E) Macrophages were left in regular media or pre-treated with 10 µg/ml CHX for 15 min and stimulated with 100 ng/ml IFNγ for 3 h. Treated macrophages were washed and subsequently cultured for 2 h in regular media, media supplemented with 10 µg/ml CHX, or anti-IFNγ neutralizing antibody (10 µg/ml) and collected for immunoblot. Duplicates from one subject are shown. (F) Quantification of pSTAT1 band intensities in E normalized to band intensity of macrophages treated with IFNγ for 3 h. (G) Human macrophages were stimulated with 100 ng/ml IFNγ for 8 h, washed, and cultured in regular media or media supplemented with 1 µM ruxolitinib for 16 h. After 16 h, cells were washed again and cultured in regular media for an additional 24 h. Cells were collected for immunoblot at indicated times. Representative blot of four replicates from two subjects. (H) Quantification of pSTAT1 band intensities in G normalized to band intensity of macrophages treated with IFNγ for 3 h. Statistical tests were determined by a single-tailed t test. *P < 0.05, **P < 0.01, and ***P < 0.001. Source data are available for this figure: SourceData F3.

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