Introduction: Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine and pivotal regulator of innate immunity. MIF is implicated in the pathogenesis of both infectious and inflammatory disorders, with elevated levels of serum MIF positively correlating with disease severity. Moreover, clinical studies have shown correlations between elevated levels of MIF and IL-1β in serum of patients with autoinflammatory disorders including Gout. To date, how MIF regulates the expression and release of IL-1 family cytokines remains unknown. 

Methods: The biological activity of MIF in murine bone marrow derived macrophages (BMDM) was inhibited using the MIF inhibitor, COR123625. Concurrently, BMDM from Mif^-/- mice were employed to evaluate the effects of MIF depletion on levels of IL-1 family cytokines. Protein expression and release of IL-1β and IL-18 were determined by western blot and ELISA. The effects of MIF inhibition in mice infected with Influenza A virus (IAV) were assessed by ELISA and survival.

Results: We show that inhibition of MIF in macrophages significantly reduced IL-1α, IL-1β and IL-18 release with no effect on secretion of TNF-α and IL-6. Moreover, inhibition of MIF specifically reduced NLRP3-mediated IL-1β and IL-18 release, as levels were unaffected following activation of the AIM2 or NLRC4 inflammasomes. Moreover, diminished IL-1 responses were independent of transcription and translation of pro-IL-1β. We next investigated the role of MIF in modulating disease during IAV infection in mice. Using our MIF inhibitor, we reveal for the first time that inhibition of MIF post-infection protected the host against severe IAV disease. 

Conclusion: Our findings reveal a novel role for MIF in the modulation of IL-1-dependent inflammatory responses, linking MIF directly to NLRP3 inflammasome activation. Findings from this study for the first time show a specific role for MIF in the release of IL-1 family cytokines highlighting the potential of targeting MIF in IL-1-dependent pathologies.