Background/Purpose:

Life-threatening hyperinflammatory syndromes caused by severe hypercytokinemia include primary (p) and secondary (s) hemophagocytic lymphohistiocytosis (HLH). Increased circulating levels of interferon gamma (IFNg) in pHLH and sHLH patients suggest a central role for this cytokine in the development and maintenance of hypercytokinemia observed in HLH.  

Methods:

C57BL/6 mice were injected i.p. on days 0, 2, 4, 7 and 9 with 50 μg of CpG-ODN 1826. Anti-mouse IFNg neutralizing mAb (XMG1.2) and rat IgG1 isotype-matched control mAb (mAb35) were injected intravenously at 100 mg/kg. Q-PCR was used to analyze inflammatory gene expression. Luminex multiplex technology was used to detect serum cytokines. Blood parameters were measured using a haematological counter. Serum concentrations of total IFNg were determined by an ELISA method developed for purpose. Serum samples were taken from 14 sHLH patients, with underlying infection demonstrated in 7 patients, (age at onset 8.6 years, interquartile range (IQR) 4.1-12.9 years; female 36%), seen at the Ospedale Pediatrico Bambino Gesù, Italy. All patients met the 2004-HLH diagnostic guidelines. 

Results:

Using a model that mimics an infection-driven sHLH, TLR9 agonism resulted in a multi-phasic production of IFNg evidenced by a spike in serum cytokine levels following each CpG-ODN injection. Therapeutic blockade of IFNg reduced body weight loss, splenomegaly, normalized white blood cell counts, significantly reversed the decrease in other laboratory parameters (e.g. platelets, haemoglobin and red blood cells) and controlled hyperferritinemia. Our study reveals that total IFNg levels, originating within organs, are 500- to 2,000-fold higher than those present in blood. Expression of IFNg induced inflammatory genes demonstrated that spleen and liver are major sites of IFNg production. Furthermore, the IFNg signature gene products, CXCL9 and CXCL10, correlate with disease severity. In patients with sHLH, sampled during active full blown disease, levels of IFNg (median 34.7 pg/mL, IQR 23.9-170.1) and IFNg inducible chemokines (CXCL9: 33598 pg/mL, IQR 3083-127687; CXCL10; 4420 pg/mL, IQR 799-8226) were markedly higher than those of patients sampled during remission following effective treatment (IFNg <3.5 pg/mL, IQR <3.5-6.5; CXCL9: 745 pg/mL, IQR 469-1098; and CXCL10; 132 pg/mL, IQR 74-157). Similar to what was found in TLR9-induced sHLH in mice, IFNg levels significantly correlated with levels of CXCL9 and CXCL10. Furthermore, levels of IFNγ, as well as of CXCL9 and CXCL10, correlated with laboratory parameters of HLH including neutrophil and platelet counts, ferritin, LDH and ALT levels. 

Conclusion:

IFNg production in the tissues is central to the hypercytokinemia causing the manifestations of the disease in mice following recurrent TLR9 repeated stimulation. Taken together with data in patients with sHLH, our observations demonstrate that IFNg appears to be the driving mediator of sHLH, support the role of CXCL9 and CXCL10 levels as a marker of the production of IFNg and indicate that the neutralization of IFNγ should be investigated as a therapeutic approach also in secondary forms of HLH.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/interferon-gamma-ifng-is-the-driving-mediator-of-secondary-hemophagocytic-lymphohistiocytosis-shlh-in-tlr9-mediated-pathogenesis-in-mice-and-is-correlated-to-disease-parameters-in-children/