JAK/STAT inhibition improves macrophage phagocytosis of bacteria

In COPD, the lower airways are colonised with bacteria that contribute to exacerbations. This may be due to defective macrophage phagocytosis. IFNγ is elevated in COPD and can suppress macrophage phagocytosis. IFNγ activates the JAK/STAT pathway, thus we hypothesise that inhibiting this pathway will ablate the IFNγ effect on macrophage phagocytosis. Human lung macrophages were treated with two structurally distinct JAK/STAT inhibitors (PF95 & PF13, 10-4-10-10M), stimulated with 10ng/ml IFNγ for 18h. Phagocytosis was measured after 4h exposure to beads, H. influenzae (HI) or S. pneumoniae (SP) . CXCL10 and IL-6 release after IFNγ or IFNγ+TNFα (10ng/ml) stimulation for 24h was measured by ELISA n=5. Cell viability was assessed by MTT. IFNγ increased bead phagocytosis by 30±6% which was not altered by PF95 or PF13. However IFNγ significantly inhibited uptake of HI by 24±9% and SP by 29±9%. Both PF95 and PF13 reversed these effects in a concentration-dependent manner [Table 1]. PF13, but not PF95, was cytotoxic at concentrations ≥10μM. Both PF95 and PF13 decreased CXCL10 release after IFNγ stimulation (EC50 0.31±0.17μM & 15±9.5nM respectively) and IFNγ+TNFα (EC50 0.57±0.2μM & 19±8.2nM respectively). Only PF13 decreased IL-6 after IFNγ or IFNγ+TNFα stimulation (EC50 0.45±0.72μM and 2.3±2.1μM respectively). View this table: Table 1. Effect of JAK/STAT inhibitors on IFNγ suppression of bacterial phagocytosis Inhibiting the JAK/STAT pathway diminishes the decrease in phagocytosis of HI and SP caused by IFNγ and decreases the release of inflammatory cytokines and has potential as a novel target in COPD.