Severe imbalance of IL-18/IL-18BP in patients with secondary hemophagocytic syndrome

Abstract

Hemophagocytic syndrome (HPS) is characterized by an uncontrolled and poorly understood activation of T-helper 1 (Th-1) lymphocytes and macrophages. We studied 20 patients with HPS secondary to infections, autoimmune disease, lymphoma, or cancer and observed that the concentrations of serum interleukin 18 (IL-18), a strong inducer of Th-1 responses, interferon gamma (IFN-gamma) production, and stimulation of macrophages and natural killer (NK) cells were highly increased in HPS but not in control patients. In contrast, concentrations of its natural inhibitor, the IL-18 binding protein (IL-18BP), were only moderately elevated, resulting in a high level of biologically active free IL-18 in HPS (4.6-fold increase compared with controls; P < .001). Free IL-18 but not IL-12 concentrations significantly correlated with clinical status and the biologic markers of HPS such as anemia (P < .001), hypertriglyceridemia, and hyperferritinemia (P < .01) and also with markers of Th-1 lymphocyte or macrophage activation, such as elevated concentrations of IFN-gamma and soluble IL-2 and tumor necrosis factor alpha (TNF-alpha) receptor concentrations. Despite high IL-18 elevation, in vitro NK-cell cytotoxicity was severely impaired in HPS patients, in part due to NK-cell lymphopenia that was observed in a majority of patients but also secondary to an intrinsic NK-cell functional deficiency. We concluded that a severe IL-18/IL-18BP imbalance results in Th-1 lymphocyte and macrophage activation, which escapes control by NK-cell cytotoxicity and may allow for secondary HPS in patients with underlying diseases.

Figure 1.

Increased IL-18 concentrations in the serum of HPS patients. (A) Total IL-18 and (B) IL-18BP concentrations were measured and (C) free IL-18 concentrations were calculated in HPS patients during the acute phase or after remission of the disease as well as in control groups composed of healthy volunteers (healthy controls) or patients suffering from infection, malignant hemopathy, or cancer without HPS (disease controls). Box plot representation, horizontal line within boxes represents median. ○ indicates outside values. *P < .01, **P ≤ .001 compared with respective controls.

Figure 2.

IL-18 concentrations follow-up in patients with HPS. Free IL-18 concentrations were calculated from IL-18 and IL-18BP measured concentrations in 12 patients with HPS at 2 different times. Patients were divided into 2 different subgroups depending on clinico-biologic evolution (A, remission n = 9; B, persistent n = 3).

Figure 3.

IL-18 mRNA concentrations in patients' PBMCs. Steady-state IL-18 mRNA concentrations were measured using RT-PCR in freshly isolated PBMCs from HPS patients and controls. Box plot representation, horizontal line within boxes represents median.

Figure 4.

Correlations between free IL-18 concentrations and biologic markers in HPS patients. Correlations were studied between initial serum-free IL-18 concentrations and the various biologic markers of HPS such as hemoglobin (Hb), polymorphonuclear cells (PMNs), platelets (plt), ferritinemia, triglyceridemia (Tg), and LDH (*P < .05, **P < .01, ***P < .001; n = 21).

Figure 5.

Concentrations of various cytokines and soluble receptors. Concentrations of IFN-γ (A), sIL-2Rα (B), sTNFR1 (C), and sTNFR2 (D) were measured in the serum of control individuals and HPS patients during the acute phase or after remission of the disease. Box plot representation, horizontal line within boxes represents median. ○ indicates outside values (*P < .05, **P ≤ .001 compared with respective controls).

Figures 6.

Correlations between various Th-1 cytokines, soluble receptors, and free IL-18 concentrations in HPS patients. Correlations were studied in HPS patients between calculated free IL-18 initial concentrations and the measured concentrations of other cytokines (*P < .01, **P < .001).

Figure 7.

Correlations between CD3–CD56⁺CD16⁺-cell numbers corresponding to NK cells and free IL-18 calculated concentrations in HPS patients during the acute phase of the disease. Correlations were studied between NK-cell numbers and free IL-18 concentrations (A), NK natural cytotoxicity (B), and antibody-dependent cell cytotoxicity (ADCC; C) in HPS and control patients. In vitro NK cytotoxicity and ADCC were studied in HPS patients (n = 7) and compared with 2 control groups (healthy controls, n = 30; and disease controls, n = 21). Box plot representation, horizontal line within boxes represents median (*P < .01, **P = .001 compared with healthy controls). ○ indicates outside values.