Divergent mechanisms of action of the inflammatory cytokines interleukin 1‐β and tumour necrosis factor‐α in mouse cremasteric venules

Protein synthesis dependency and the role of endogenously generated platelet activating factor (PAF) and leukotriene B4 (LTB4) in leukocyte migration through interleukin‐1β (IL‐1β)‐ and tumour necrosis factor‐α (TNFα)‐stimulated mouse cremasteric venules was investigated using established pharmacological interventions and the technique of intravital microscopy. Based on previously obtained dose‐response data, 30 ng rmIL‐1β and 300 ng rmTNFα were injected intrascrotally (4 h test period) to induce comparable levels of leukocyte firm adhesion and transmigration in mouse cremasteric venules. Co‐injection of the mRNA synthesis inhibitor, actinomycin D (0.2 mg kg−1), with the cytokines significantly inhibited firm adhesion (49±13.6%) and transmigration (67.2±4.2%) induced by IL‐1β, but not TNFα. In vitro, TNFα (1–100 ng ml−1), but not IL‐1β, stimulated L‐selectin shedding and increased β2 integrin expression on mouse neutrophils, as quantified by flow cytometry. The PAF receptor antagonist, UK‐74,505 (modipafant, 0.5 mg kg−1, i.v.), had no effect on adhesion induced by either cytokine, but significantly inhibited transmigration induced by IL‐1β (66.5±4.5%). The LTB4 receptor antagonist, CP‐105,696 (100 mg kg−1, p.o.), significantly inhibited both IL‐1β induced adhesion (81.4±15.2%) and transmigration (58.7±7.2%), but had no effect on responses elicited by TNFα. Combined administration of the two antagonists had no enhanced inhibitory effects on responses induced by either cytokine. The data indicate that firm adhesion and transmigration in mouse cremasteric venules stimulated by IL‐1β, but not TNFα, is protein synthesis dependent and mediated by endogenous generation of PAF and LTB4. Additionally, TNFα but not IL‐1β, can directly stimulate mouse neutrophils in vitro. The findings provide further evidence to suggest divergent mechanisms of actions of IL‐1β and TNFα, two cytokines often considered to act via common molecular/cellular pathways. British Journal of Pharmacology (2002) 137, 1237–1246. doi:10.1038/sj.bjp.0704981