Janus kinase inhibitors block the IL-12 and IFN-γ response in peripheral blood mononuclear cells (PBMCs) from STAT4 risk patients with systemic lupus erythematosus (SLE). (A) Healthy donor PBMCs were treated with serial dilutions of the JAK2 selective (JAK2i), the TYK2 selective (TYK2i) and the pan-JAK inhibitor (pan-JAKi) before being stimulated with 5 ng/mL IL-12, 0.1 ng/mL IFN-γ or 200 U/mL IFN-α for 20 min. IL-12-stimulated cells were preactivated with PHA/IL-2. Phosphorylation of STAT4 (pSTAT4) and STAT1 (pSTAT1) was determined by flow cytometry in IL-12-stimulated cells and IFN-γ or IFN-α-stimulated cells, respectively. Data (mean±SD of two individuals) from IL-12 and IFN-α-stimulated cells are shown for CD3 + T cells and from IFN-γ-stimulated cells for monocytes. (B) IC 50 values for each inhibitor. (C–E) PBMCs from healthy donors (HD), patients with SLE homozygous for the protective STAT4 allele (G/G) and patients with SLE carrying one or two STAT4 risk alleles (G/T+T/T) were incubated with 200 nM TYK2i (C, D), 70 nm JAK2i or 30 nM pan-JAKi (E). (C, D) Inhibition of IL-12-induced pSTAT4 in CD8 + T cells (C) and reduction in the frequency of IFN-γ + memory CD45RO + CD57 – CD8 + T cells (D). (E) Inhibition of IFN-γ-induced pSTAT1 in monocytes. (C–E) Open triangles and squares denote G/T and T/T patients with SLE, respectively.