IL-1ra and IL-1 production in human oral mucosal epithelial cells in culture: differential modulation by TGF-beta1 and IL-4

Regulatory cytokines mediate the participation of oral mucosal epithelial cells (OMEC) in local immune responses. The aim of this study was to characterize the isoforms of IL-1 receptor antagonist (IL-1ra) in cultured human primary OMECs and to compare its production with that of IL-1 alpha (IL-1alpha) and IL-1 beta (IL-1beta). Western blot analysis showed that IL-1ra was 22 kDa in size hence slightly smaller than monocyte IL-1ra (25 kDa). A minor form of 20 kDa was also found in unstimulated cell culture lysates. In culture supernatants, IL-1 bioactivity increased after IL-1ra neutralization, indicating that the baseline production of IL-1ra is biologically relevant. Immunohistochemistry showed a relation between IL-1ra and involucrin expressions, suggesting that intracytoplasmic IL-1ra may be involved in cell terminal differentiation. In unstimulated culture lysates, there was far more IL-1ra than IL-1alpha and IL-1beta. TGF-beta1 markedly increased the IL-1ra/IL-1beta ratio from 93.6 : 1 to 300 : 1. IL-4, which is generally described as an anti-inflammatory cytokine, increased IL-1 but not IL-1ra production. TNF-alpha increased intracellular production of the three IL-1 members. IL-1ra levels were lower in supernatants than in lysates of cultured cells. Our results show that human OMECs constitutively produce significant amounts of a biologically active form of IL-1ra. TGF-beta1 mu(p)-regulation points to a positive amplification loop and IL-4 to a down-regulation loop, both including Th2 cells and OMECs. They may be important in oral tolerance and IgA production, respectively.