IFN-γ Signature Distinguishes Pediatric Hemophagocytic Lymphohistiocytosis from Sepsis and SIRS

Hemophagocytic lymphohistiocytosis (HLH), severe sepsis, and persistent systemic inflammatory response syndrome are all conditions defined by excessive immune activation that may progress rapidly and are associated high risk of death without early introduction of appropriate therapy.

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome characterized by pathologic immune activation in which prompt recognition and initiation of immune suppression is essential for survival. Children with HLH have many overlapping clinical features with critically ill children with sepsis and systemic inflammatory response syndrome (SIRS) in whom alternative therapies are indicated.

A large team of Pediatric Hematologists at the Baylor College of Medicine (Houston, TX, USA) collected sand processed blood samples of 40 patients with HLH and 47 pediatric patients with severe sepsis or SIRS. Plasma protein levels of 135 analytes representing cytokines, chemokines, and growth factors were determined using Milliplex MAP antibody panels (Millipore, Burlington, MA, USA) for the MagPix instrument (Luminex Corporation, Austin, TX, USA). Ferritin and interleukin-18 (IL-18) were analyzed in independent MagPix assays.

Peripheral blood mononuclear cells were sorted for CD3, CD4, CD8), and CD68 using the BD Aria Fusion (BD Bioscience, Franklin Lakes, NJ, USA). cDNA was prepared from CD3⁺8⁺ and CD3⁻68⁺ populations with the Nugen Ovation Pico WTA System V2 (Nugen, Redwood City, CA, USA). Gene expression data were generated using Affymetrix GeneChip Human Transcriptome Array 2.0 (Affymetrix, Santa Clara, CA, USA).

The scientists reported that 15 of 135 analytes were significantly different in HLH plasma compared with SIRS/sepsis, including increased interferon-γ (IFN-γ)–regulated chemokines CXCL9, CXCL10, and CXCL11. Furthermore, a 2-analyte plasma protein classifier including CXCL9 and interleukin-6 was able to differentiate HLH from SIRS/sepsis. Gene expression in CD8⁺ T cells and activated monocytes from blood were also enriched for IFN-γ pathway signatures in peripheral blood cells from patients with HLH compared with SIRS/sepsis.

Of the 40 pediatric HLH subjects, nine had biallelic gene mutations known to cause HLH (or monoallelic X-linked SH2D1A), four had single allele variants associated with HLH, and 11 had variants of uncertain significance in genes associated with immune functions potentially associated with immune dysregulation and HLH susceptibility.

The authors concluded that in their study they had identified differential expression of inflammatory proteins as a diagnostic strategy to identify critically ill children with HLH. Comprehensive unbiased analysis of inflammatory plasma proteins and global gene expression demonstrated that IFN-γ signaling is uniquely elevated in HLH. The study was published on September 10, 2021 in the journal Blood Advances.

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