Increased interleukin-10 and macrophage inflammatory protein-1α release from blood monocytes ex vivo during late-phase response to allergen in asthma

Background: We determined the effect of late-phase responses to allergen challenge of mildly allergic asthmatic patients on the expression and release of the cytokines IL-IO and MIP-1 alpha from peripheral blood monocytes. Methods: Sixteen mildly allergic asthmatics were exposed to increasing concentrations of allergen aerosol. Nine demonstrated an early response alone (single responders), while seven had an early followed by a late response (dual responders). Monocytes were isolated from venous blood before and 24 h after allergen challenge, and placed in short-term culture for determination of IL-10 mRNA expression by reverse-transcription polymerase chain reaction and protein release. MIP-1 alpha protein release was measured by radioimmunoassay. Results: IL-10 mRNA expression was significantly higher in dual responders than early responders alone, for unstimulated monocytes or for monocytes exposed to lipopolysaccharide or IL-1 beta. In addition, the release of IL-10 and MIP-1 alpha from monocytes of dual responders was also enhanced. Conclusions: Circulating monocytes are primed to release more of the cytokines, IL-IO and MIP-1 alpha, in dual but not in single responders, at 24 h after allergen. They may contribute to allergen-induced inflammatory responses in the airways.