Dexamethasone inhibits the production of macrophage inflammatory protein 2 in the leukocytes in rat allergic inflammation.

In the air pouch-type allergic inflammation model in rats, when the infiltrated leukocytes in the pouch fluid collected 4 h after antigen challenge were incubated, neutrophil chemotactic activity in the conditioned medium increased time-dependently. They produced neutrophil chemotactic factors, viz. leukocyte-derived neutrophil chemotactic factor (LDNCF)-2, a major component, and LDNCF-1, a minor component. When the infiltrated leukocytes were incubated in the presence of dexamethasone, neutrophil chemotactic activity in the conditioned medium decreased in a concentration-dependent manner, and production of LDNCF-2 and LDNCF-1 was inhibited. Because purified LDNCF-2 had been found to be identical with rat macrophage inflammatory protein 2 (MIP-2), effects of dexamethasone on the level of MIP-2 mRNA in the leukocytes were investigated. Using the reverse transcription-polymerase chain reaction technique, it was demonstrated that dexamethasone suppressed the level of MIP-2 mRNA in the leukocytes. These results indicate that dexamethasone inhibits MIP-2 production at the transcription level.