Characterization and biologic activities of recombinant rat soluble interleukin-6 receptor

Natural Glycoforms of Human Interleukin 6 Show Atypical Plasma Clearance

A library of glycoforms of human interleukin 6 (IL‐6) comprising complex and mannosidic N‐glycans was generated by semisynthesis. The three segments were connected by sequential native chemical ligation followed by two‐step refolding. The central glycopeptide segments were assembled by pseudoproline‐assisted Lansbury aspartylation and subsequent enzymatic elongation of complex N‐glycans. Nine IL‐6 glycoforms were synthesized, seven of which were evaluated for in vivo plasma clearance in rats and compared to non‐glycosylated recombinant IL‐6 from E. coli. Each IL‐6 glycoform was tested in three animals and reproducibly showed individual serum clearances depending on the structure of the N‐glycan. The clearance rates were atypical, since the 2,6‐sialylated glycoforms of IL‐6 cleared faster than the corresponding asialo IL‐6 with terminal galactoses. Compared to non‐glycosylated IL‐6 the plasma clearance of IL‐6 glycoforms was delayed in the presence of larger and multibranched N‐glycans in most cases

Serum interleukin-6 soluble receptor in relation to interleukin-6 in stroke patients

Cerebral ischemia triggers interleukin-6 (IL-6) release into blood. IL-6 is a key mediator of acute phase reaction. Markers of acute phase reaction (C-reactive protein, fibrinogen, fever) have been linked to poor prognosis in stroke patients. Interleukin-6 soluble receptor (sIL-6R) can potentiate IL-6 pro-inflammatory activity. The aim of this study was to investigate the relationship between IL-6 and sIL-6R in stroke patients. Serum cytokine levels were measured in 18 stroke patients and 13 controls using the ELISA method. On the second day of stroke, IL-6 levels were significantly higher in stroke patients than in controls; sIL-6R levels did not differ significantly between groups. Three months after stroke, IL-6 levels did not differ significantly between groups; sIL-6R levels were significantly decreased in stroke patients when compared with that in controls and with levels in acute phase of stroke. Decreased sIL-6R early after stroke might reflect a regulatory mechanism attenuating inflammatory response.

Cytokine balance in the lungs of patients with acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) involves an intense inflammatory response in the lungs, with accumulation of both pro- and antiinflammatory cytokines in bronchoalveolar lavage fluid (BALF). Our goal was to determine how the balance between pro- and antiinflammatory mediators in the lungs changes before and after the onset of ARDS. We identified 23 patients at risk for ARDS and 46 with established ARDS and performed serial bronchoalveolar lavage (BAL). We used immunoassays to measure tumor necrosis factor alpha (TNF-alpha) and soluble TNF-alpha receptors I and II; interleukin 1 beta (IL-1 beta), IL-1 beta receptor antagonist, and soluble IL-1 receptor II; IL-6 and soluble IL-6 receptor; and IL-10. We used sensitive bioassays to measure net TNF-alpha, IL-1 beta, and IL-6 activity. Although individual cytokines increased before and after onset of ARDS, greater increases occurred in cognate receptors and/or antagonists, so that molar ratios of agonists/antagonists declined dramatically at the onset of ARDS. The molar ratios remained low for 7 d or longer, limiting the activity of soluble IL-1 beta and TNF-alpha in the lungs at the onset of ARDS. This significant antiinflammatory response early in ARDS may provide a key mechanism for limiting the net inflammatory response in the lungs.

Reciprocal actions of interleukin-6 and brain-derived neurotrophic factor on rat and mouse primary sensory neurons

In low-density, serum-free cultures of neurons from embryonic rat dorsal root ganglia, interleukin-6 supports the survival of less than one third of the neurons yet virtually all of them bear interleukin-6 alpha-receptors. A finding that might explain this selectivity is that interleukin-6 acts on sensory neurons in culture through a mechanism requiring endogenous brain-derived neurotrophic factor. Antibodies or a trkB fusion protein that block the biological activity of brain-derived neurotrophic factor synthesized by dorsal root ganglion neurons also block the survival-promoting actions of interleukin-6 on these neurons. Two results indicate that interleukin-6 influences synthesis of brain-derived neurotrophic factor in adult dorsal root ganglion neurons. Intrathecal infusion of interleukin-6 in rats increases the concentration of brain-derived neurotrophic factor mRNA in rat lumbar dorsal root ganglia. The induction of brain-derived neurotrophic factor in dorsal root ganglion neurons that is seen after nerve injury in rats or wild-type mice is severely attenuated in mice with null mutation of the interleukin-6 gene. In brief, the ability of interleukin-6 to support the survival of embryonic sensory neurons in vitro depends upon the presence of endogenous brain-derived neurotrophic factor and the induction of brain-derived neurotrophic factor in injured adult sensory neurons depends upon the presence of endogenous interleukin-6.

Interleukin-6 (IL-6) and its soluble receptor support survival of sensory neurons

The cytokine interleukin-6 (IL-6) has multiple functions in the immune and hematopoietic systems. IL-6 is related to ciliary neurotrophic factor (CNTF), a trophic factor for motoneurons, sensory dorsal root ganglion (DRG) neurons, and other neuronal subpopulations. Both act via related receptor complexes, consisting of one ligand-specific alpha-receptor subunit (IL-6R and CNTFR, respectively) and two signal-transducing receptor components. Even though IL-6 is expressed by neurons and glia, the functions of IL-6 in the nervous system are poorly understood. Here, we report that exogenous human IL-6 promotes the survival of dissociated newborn rat DRG neurons in vitro if supplemented with soluble human IL-6-alpha-receptor. The dosages of human IL-6 and soluble human IL-6R necessary to achieve neurotrophic effects could be reduced markedly by linking ligand and alpha-receptor component in a designer cytokine. Furthermore, we show that newborn rat DRG neurons express and secrete bioactive IL-6. Endogenously secreted IL-6 does not enhance survival of these neurons in vitro, suggesting that DRG neurons do not sufficiently express cell surface IL-6R. Exogenously added soluble rat IL-6R rendered DRG neurons responsive to secreted IL-6. Our results indicate an autocrine function of IL-6 in DRG neuron survival which depends on membrane-bound or soluble IL-6R as a neurotrophic cofactor.

Hyperventilation induces release of cytokines from perfused mouse lung

Artificial mechanical ventilation represents a major cause of iatrogenic lung damage in intensive care. It is largely unknown which mediators, if any, contribute to the onset of such complications. We investigated whether stress caused by artificial mechanical ventilation leads to induction, synthesis, and release of cytokines or eicosanoids from lung tissue. We used the isolated perfused and ventilated mouse lung where frequent perfusate sampling allows determination of mediator release into the perfusate. Hyperventilation was executed with either negative (NPV) or positive pressure ventilation (PPV) at a transpulmonary pressure that was increased 2.5-fold above normal. Both modes of hyperventilation resulted in an approximately 1.75-fold increased expression of tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) mRNA, but not of cyclooxygenase-2 mRNA. After switching to hyperventilation, prostacyclin release into the perfusate increased almost instantaneously from 19 +/- 17 pg/min to 230 +/- 160 pg/min (PPV) or 115 +/- 87 pg/min (NPV). The enhancement in TNFalpha and IL-6 production developed more slowly. In control lungs after 150 min of perfusion and ventilation, TNFalpha and IL-6 production was 23 +/- 20 pg/min and 330 +/- 210 pg/min, respectively. In lungs hyperventilated for 150 min, TNFalpha and IL-6 production were increased to 287 +/- 180 pg/min and more than 1,000 pg/min, respectively. We conclude that artificial ventilation might cause pulmonary and systemic adverse reactions by inducing the release of mediators into the circulation.