The role of TNFα in the pathogenesis of atherosclerosis is incompletely understood. TNFα blockade reduces the severity of various autoimmune diseases and the often related atherosclerosis. However, excessively released TNFα is only one component of the hyperactive innate immune system in such diseases. To provide more insight into the role of TNFα in the induction of inflammation, we explored the effects of TNFα blockade in human whole blood.
TLR4/NLPR3 inflammasome challenges were applied to induce an inflammatory response. For this purpose, whole blood was incubated 4 hours with LPS and aluminium hydroxide (Alhydrogel). TNFα blockade was evaluated in vitro (LPS/Alhydrogel challenge in whole blood of 4 healthy human subjects, +concentration range of adalimumab) and ex vivo (LPS/Alhydrogel challenge in whole blood of 13 healthy human subjects receiving a single subcutaneous (sc) dose of 40 mg adalimumab). Cytokine release was evaluated in culture supernatants.
In vitro, TNFα blockade strongly reduced TNFα levels detected; -97±1% at the lowest adalimumab concentration (0.3125 μg/mL). TNFα blockade did not affect LPS/Alhydrogel-induced IL-6, IL-1β and IL-18 release, but reduced IFNγ release; maximally -93±4% at 5 μg/mL adalimumab. A single sc adalimumab dose in healthy subjects reduced LPS/Alhydrogel-induced TNFα levels (maximally -98±1% on day 4, and still -58±59% on day 64; versus baseline). IL-6, IL-1β and IL-8 release were not reduced after anti-TNFα treatment. The effect of TNFα blockade on IFNγ release could not be reliably estimated due to highly variable IFNγ levels, especially between genders (baseline IFNγ levels 1248±1771 and 140±283 pg/mL, males vs females).
TNFα is a major inducer of NFκB-driven cytokine gene transcription, but TNFα blocking did not reduce LPS/Alhydrogel-induced release of IL-1β, IL-6, IL-8 or IL-18 by primary human cells. This suggests that primary TLR4- and inflammasome-mediated signalling is sufficient to drive secretion of these cytokines. However, in vitro TNFα blockade did impair IFNγ release. Since IFNγ is a key factor in atherogenesis, exerting both pro- and anti-atherogenic properties, our data warrant further mechanistic investigation of the role of TNFα and anti-TNFα therapies in atherosclerosis.
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