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

Abstract

1 Protein synthesis dependency and the role of endogenously generated platelet activating factor (PAF) and leukotriene B 4 (LTB 4) 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. 2 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. 3 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. 4 In vitro, TNFα (1-100 ng ml -1), but not IL-1β, stimulated L-selectin shedding and increased β 2 integrin expression on mouse neutrophils, as quantified by flow cytometry. 5 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%). 6 The LTB 4 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. 7 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 LTB 4. 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.