OBJECTIVE

Leukotriene A(4) (LTA(4)) hydrolase catalyzes the final step in the synthesis of leukotriene B(4) (LTB(4)). TH-1- and TH-2-derived cytokines may regulate LTB(4) synthesis by monocytes through their actions on the expression of LTA(4) hydrolase.

METHODS

Freshly isolated monocytes were incubated with pro- and anti-inflammatory cytokines for 36 h. mRNA expression was determined by Northern blot, protein expression was determined by Western blot and LTB(4) synthesis was determined by ELISA.

RESULTS

Interferon-gamma (a TH-2-derived cytokine) increased significantly LTA(4) hydrolase mRNA expression, whereas interleukin (IL)-4 and IL-13 (both TH-2-derived cytokines) decreased LTA(4) hydrolase mRNA expression in these cells. The same effects were seen on the expression of immunoreactive LTA(4) hydrolase after incubating the monocytes with either TH-1- or TH-2-derived cytokines. The monocyte-derived cytokine IL-1 beta did not show any significant effect on LTA(4) hydrolase mRNA expression. When LTB(4) release was measured, both IL-1 beta and interferon-gamma significantly increased LTB(4) production by monocytes, while TH-2 cytokines (IL-4 and IL-13) decreased it.

CONCLUSIONS

The opposing effects of TH-1- and TH-2-derived cytokines on the expression of LTA(4) hydrolase mRNA may regulate LTB(4) synthesis by monocytes during inflammation.