Neutrophils with myeloid derived suppressor function deplete arginine and constrain T cell function in septic shock patients

Abstract

IntroductionImpaired T cell function in sepsis is associated with poor outcome, but the mechanisms are unclear. In cancer, arginase-expressing myeloid derived suppressor cells (MDSCs) deplete arginine, impair T cell receptor CD3 zeta-chain expression and T cell function and are linked to poor clinical outcome, but their role during acute human infectious disease and in particular sepsis remains unknown. Hypoarginemia is prevalent in sepsis. This study aimed to determine whether neutrophils that co-purify with PBMC express arginase, and if arginine depletion constrains T cell CD3 zeta-chain expression and function in human sepsis.MethodsUsing flow cytometry, cell culture, HPLC, arginase activity and mRNA detection, our study examined whether neutrophils, with reduced buoyant density isolated in the Ficoll interface, metabolise L-arginine and suppress T cell proliferation in sepsis. A total of 35 sepsis patients (23 with septic shock) and 12 hospital controls in a tertiary referral hospital in tropical Australia were evaluated.ResultsOnly sepsis patients had interphase neutrophils, neutrophils co-purifying with mononuclear cells (≤1.077 specific gravity). The percentage of interphase neutrophils in sepsis was proportional to sepsis severity and correlated with plasma IL-6 concentrations. Ex vivo, sepsis-derived interphase neutrophils expressed arginase, metabolised culture L-arginine and suppressed T cell proliferation and CD3 zeta-chain expression. In vivo, in septic shock there was a longitudinal inverse association between interphase neutrophil number and CD3 zeta-chain expression. Depletion or inhibition of interphase neutrophils in vitro restored zeta-chain expression and T cell function.ConclusionsFor the first time during an acute human infection, interphase neutrophils that express arginase were found to circulate in sepsis, in proportion to disease severity. These neutrophil-MDSCs impair T cell CD3 zeta-chain expression and T cell function via L-arginine metabolism, and likely contribute to the T cell dysfunction seen in sepsis. Modulation of neutrophil-MDSC or their downstream effects warrant consideration as targets for novel adjunctive therapies in sepsis.Electronic supplementary materialThe online version of this article (doi:10.1186/cc14003) contains supplementary material, which is available to authorized users.

A Subset of Neutrophils Expressing Markers of Antigen-Presenting Cells in Human Visceral Leishmaniasis

“…We made the surprising observation that a subset of circulating neutrophils express markers of antigen presentation, including major histocompatibility complexclass II and costimulatory molecules CD80 and CD86 in subjects with VL. These cells migrated in the low-density fraction of peripheral blood leukocytes, a fraction that harbors mononuclear leukocytes and a recently described LDG population, which is best studied in patients with malignancy or autoimmune disease [31]. We showed these cells are neutrophils according to surface markers, a characteristic microscopic appearance, and the presence of a neutrophil-specific transcript.…”

“…These LDGs are activated and secrete type I IFNs, tumor necrosis factor α, and IFN-γ but have diminished capability to phagocytose [9]. LDGs in patients with septic shock reportedly express arginase and the zeta chain of the T-cell receptor (CD247), and the numbers of these neutrophils in the PBMC fractions correlates with the severity of disease [31]. Finally, PBMC fractions from Ethiopian patients with active VL were found to contain CD15 + neutrophils with high levels of arginase.…”

“…It can be debated whether LDGs are the same as the so-called G-MDSCs, suppressive myeloid cells with properties of immature granulocytic lineage that also migrate in the low-density leukocyte fraction [31,33]. Such cells can be induced by transforming growth factor-beta, which is amply present in the circulation of individuals with VL [26,33].…”

The Prognostic Value of the Myeloid-Mediated Immunosuppression Marker Arginase-1 in Classic Hodgkin Lymphoma

“…The inflammatory environment may contribute to the accumulation of both mature neutrophils and MDSC. PMN from healthy donors activated with N-formil-L-methyonil-L-leucyl-Lphenylalanine co-purify with PBMC and suppress T-cells in a dose-dependent manner [38], similarly to mature neutrophils isolated from patients affected by sepsis [39] or mature neutrophils isolated from volunteers treated with LPS [34]. In absence of reliable markers to distinguish in human between normal mature neutrophils and G-MDSC, we hypothesized that aberrant function of HL-N could be due to a chronic stimulation (as suggested by CD11b expression) to sequentially downregulated T-cell function and inhibited effector responses during the transition to memory cells [40].…”

Influence of different fluid resuscitation techniques on the number of myeloid-derived suppressor cells in rats

“…MDSCs were first discovered in tumors where they were found to be involved in the mechanism of tumor immune escape. In recent years, the interest in MDSCs has been extended to infections and traumatic hemorrhagic shock (Cuenca et al, 2011;Darcy et al, 2014;Köstlin et al, 2014;Yao et al, 2015).…”