Monocytes From Patients With Macrophage Activation Syndrome and Secondary Hemophagocytic Lymphohistiocytosis Are Hyperresponsive to Interferon Gamma

Objective To investigate the activation of the IFN gamma signaling pathway in monocytes of patients with secondary hemophagocytic lymphohistiocytosis (sHLH)/macrophage activation syndrome (MAS) and to evaluate whether levels of phosphorylated STAT1 represent a biomarker for the identification of patients at early stages of the disease. Methods Fresh whole blood samples from pediatric patients with active sHLH/MAS, not receiving (n=10) and receiving glucocorticoids (n=14) at time of sampling, were prospectively collected. As disease control groups, patients with active systemic juvenile idiopathic arthritis (sJIA) without MAS, patients with sHLH/MAS in remission and patients with other rheumatic diseases were also sampled. Whole blood cells were left unstimulated or stimulated with increasing concentrations of IFN gamma for 10 minutes and the intracellular Tyrosine (701)-phosphorylated STAT1 (pSTAT1) levels were evaluated in monocytes by flow cytometry. Results Monocytes from untreated sHLH/MAS patients showed significantly higher basal levels of pSTAT1 compared to those observed in monocytes from glucocorticoid-treated sHLH/MAS patients and from all the other disease controls. In addition, a significant increase in responsiveness to IFN gamma, as assessed by increased levels of pSTAT1 following ex vivo stimulation, was observed in monocytes from untreated sHLH/MAS patients. pSTAT1 levels in monocytes distinguished patients with sHLH/MAS not treated with glucocorticoids from patients with active sJIA or with other rheumatic diseases [AUC, 0.93; 95% confidence interval 0.85-1.00, pIFNG mRNA levels in whole blood cells, circulating IFN gamma levels and pSTAT1 levels in sHLH/MAS monocytes were found. Conclusion Our data demonstrating higher basal levels of pSTAT1 as well as a hyperreactivity to IFN gamma stimulation in monocytes from patients with sHLH/MAS point to perturbations in the activation of downstream IFN gamma signaling pathway as a contributor to the hyperinflammation occurring in these patients. Finally, the observation that glucocorticoids affect pSTAT1 levels in vivo, makes it difficult to consider the measurement of pSTAT1 levels as a biomarker to identify patients at early stages of sHLH/MAS in clinical practice.

Automated summary

This study found that untreated sHLH/MAS patients had higher levels of phosphorylated STAT1 in monocytes compared to glucocorticoid-treated patients, indicating a hyperreactivity to IFN gamma stimulation. These findings suggest that pSTAT1 levels may serve as a potential biomarker for early identification of sHLH/MAS.