Fig. 2: CXCL10 is upregulated by monocytes in response to IFN-γ released by antigen-specific T cells.

a, Schematic of proposed mechanism of CXCL10 transcript upregulation. On spike stimulation of whole blood, antigen presenting cells (APCs) present spike peptides to antigen-specific T cells that subsequently release IFN-γ. IFN-γ release can be quantified by ELLA, ELISpot or flow cytometry. Next, IFN-γ stimulates monocytes, which, in turn, upregulate CXCL10 mRNA, which can be detected by the qTACT/dqTACT assays. Figure created with Biorender.com. b, Only monocytes upregulate CXCL10 in response to IFN-γ and TNF-α. Whole blood was stimulated with DMSO (Neg) or IFN-γ + TNF-α in the presence of brefeldin/Monensin (BFA/Mon). CXCL10/IP-10 positive T cells (T), B cells (B), natural killer cells (NK), natural killer T cells (NK-T), monocytes (Mono) and neutrophils (Neutro) were quantified using flow cytometry. P values were calculated using a two-sided Wilcoxon matched-pairs signed rank test. n = 4 biologically independent samples. c, Both monocytes and neutrophils release CXCL10/IP-10 on SpG stimulation. Whole blood was stimulated with DMSO (Neg) or a spike peptide pool (SpG) in the absence (left panel) or presence (right panel) of BFA/Mon. CXCL10 positive T, B, NK, NK-T, Mono and Neutro were quantified using flow cytometry. P values were calculated using a two-sided Wilcoxon matched-pairs signed rank test. n = 4 biologically independent samples. d, Monocytes, and not neutrophils, upregulate CXCL10/IP-10 in response to SpG. Whole blood was simulated with DMSO (Neg) or a spike peptide pool (SpG) overnight with BFA/Mon added for the last 4 h. CXCL10 positive Monocytes and Neutrophils were quantified using flow cytometry. P values were calculated using a two-sided Wilcoxon matched-pairs signed rank test (P = 0.015625). n = 7 biologically independent samples. e, CXCL10 mRNA is upregulated in monocytes on stimulation with spike peptides. Monocytes and neutrophils were sorted from whole blood after overnight stimulation with spike peptides or DMSO control. RNA was extracted from the cells and the relative CXCL10 mRNA expression was determined using the qTACT assay. P values were calculated using a two-sided Wilcoxon matched-pairs signed rank test (P = 0.03125). n = 7 biologically independent samples. For b–e, the box bounds represent the first quartile (bottom), median (center) and the third quartile (top). The whiskers represent the range of samples up to 1.5 times the interquartile range. Beyond this point, samples are shown as outliers.