In Vivo Interleukin-6 Protects Neutrophils from Apoptosis in Osteomyelitis

Abstract

Polymorphonuclear neutrophils are critical for resolution of bacterial infections. In tissues, most of the neutrophils quickly die through apoptosis. Using propidium iodide DNA staining and DNA gel electrophoresis, we found that spontaneous apoptosis of neutrophils from patients suffering osteomyelitis (n ‫؍‬ 52) was significantly decreased in relation to control neutrophils (n ‫؍‬ 20) (40.2% ؎ 25.2% versus 54.5% ؎ 23.5%; P < 0.03). Incubation of neutrophils from normal volunteers with sera from patients with osteomyelitis reduced apoptosis from 79.1% ؎ 14.8% in control sera to 62.2% ؎ 18.7% in osteomyelitis sera. A significant increase of serum interleukin-6 (IL-6) and IL-1␣ was found in osteomyelitis (IL-6, 8.8 ؎ 11.9 pg/ml versus 1.8 ؎ 1.2 pg/ml in controls [P < 0.004]; IL-1␣, 3.8 ؎ 6.4 pg/ml versus 1.0 ؎ 2.2 pg/ml in controls [P < 0.02]). No differences in the levels of other cytokines, such as tumor necrosis factor alpha, were found. There was an inverse correlation between IL-6 levels and neutrophil apoptosis (r ‫؍‬ ؊0.855; P < 0.007), but this was not the case for other cytokines. The antiapoptotic effect of the osteomyelitis sera was reversed with anti-IL-6 antibodies (P < 0.03) and was reproduced with recombinant human IL-6 (P < 0.001). The longer life span of neutrophils in osteomyelitis induced by IL-6 could contribute to the tissue damage that occurs in these chronic bone infections.

Tumor‐derived macrophage migration inhibitory factor modulates the biology of head and neck cancer cells via neutrophil activation

“…For instance, IL-8 and IL-6, both of which are present in considerable amounts in FaDu SN can prolong the lifespan of neutrophils. 27,28 Similarly, growth factors such as epidermal growth factor, fibroblast growth factor or vascular endothelial growth factor are known to activate the Phosphatidylinositol-3-Kinase (PI3K) pathway, 29 consequently inhibiting apoptosis. Therefore, it is plausible that because of the presence of other prosurvival mediators in tumor-conditioned medium, the inhibition of MIF alone would not result in dramatic effects on neutrophil apoptosis.…”

Bax gene G(-248)A promoter polymorphism is associated with increased lifespan of the neutrophils of patients with osteomyelitis

“…IL-6 enhances the expression of the antiapoptotic proteins Mcl-1, A1, and Bcl-X l and inhibits constitutive Bax expression, therefore enhancing the antiapoptotic effect of A allele of the G(-248)A bax promoter polymorphism on peripheral neutrophils of patients with OM. 8,33,38,39 Neutrophils with an extended lifespan in the infected bone may help to perpetuate the bone infection by release of their proteolytic enzymes.…”

“…Cell death and apoptosis of neutrophils from patients with OM and carriers and noncarriers of the A allele were significantly decreased in relation to controls, as we previously reported. 39 Cell death rate for the AA group differs from that in the heterozygous GA (15.2% Ϯ 5.4% vs. 26.8% Ϯ 18.2%, P ϭ .066) and the wild-type GG groups (15.2% Ϯ 5.4% vs. 50.2% Ϯ 26.5%, P ϭ .107) by PI staining (Fig. 2A).…”

“…Neutrophils were purified by Ficoll-Hypaque (Lymphoprep, Axis-Shield Poc AS, Oslo, Norway) centrifugation as previously described. 39 Cells collected from the gradient interface contained more than 95% neutrophils by Coulter identification and were more than 95% viable by trypan blue exclusion. Neutrophils were isolated before each experiment and used immediately.…”

“…[33][34][35][36][37][38] Our group recently showed that the apoptosis of peripheral neutrophils from patients with OM was decreased in relation to healthy controls and that this effect seemed to be the result, at least in part, of the high levels of circulating IL-6. 39 In the present work we tried to determine whether the bax G(-248)A promoter polymorphism (rs 4645878) could play a similar role in reducing apoptosis of neutrophils from patients with OM, perhaps leading to impaired resolution of the bone infection.…”