IL-4 reciprocally regulates IL-1 and IL-1 receptor antagonist expression in human monocytes.

Activation of human monocytes with LPS induces coordinate expression of a number of cytokine genes, including IL-1 alpha, IL-1 beta, TNF-alpha, IL-6, and IL-8. The T cell-derived lymphokine, IL-4, inhibits expression of these genes in monocytes, suggesting that it may be an important physiologic regulator of cytokine production. We have previously shown that IL-4 reduces steady state messenger RNA (mRNA) levels for IL-1 beta in human monocytes by decreasing both IL-1 beta transcription and the t1/2 of newly formed IL-1 beta mRNA transcripts. In the present study, we extend these findings to show that IL-4 similarly accelerates the turnover of IL-6 mRNA in LPS-stimulated monocytes. However, this inhibition of cytokine expression and dramatic increase in the decay rate of cytokine mRNA does not extend to all LPS-inducible genes because IL-4 treatment did not inhibit the expression or accelerate the turnover of mRNA for the IL-1 receptor antagonist (IL-1ra) in the same cells. Although IL-1 beta and IL-1Ra are both LPS-inducible genes, they displayed distinct temporal patterns of expression. Peak steady state mRNA levels for IL-1ra lagged significantly behind that of IL-1 beta, suggesting a possible endogenous mechanism for limiting IL-1 biologic activity. Furthermore, although IL-4 suppressed expression of both IL-1 beta and IL-6, it up-regulated synthesis of IL-1ra mRNA and protein. Thus, IL-4 inhibits production of the proinflammatory cytokine, IL-1 beta, while concomitantly enhancing synthesis of the IL-1ra in activated human monocytes.