IL-13 EXPRESSION AT THE SITES OF ALLERGEN CHALLENGE IN PATIENTS WITH ASTHMA

Atopic asthma is characterized by inflammatory responses of the airway and is associated with up-regulation of Th2 cytokines, notably IL-4 a nd IL-5. A recently described human cytokine, IL-13, is a potent in vi tro modulator of various cell types, including monocytes, B cells, and endothelial cells. Similar to IL-4, it is also involved in the induct ion of IgE synthesis. However, the in vivo expression and function of IL-13 and its relation to disease remain to be defined. Using a segmen tal allergen challenge model, we have examined the in vivo expression of IL-13 in the bronchoalveolar ravage (BAL) cells of atopic patients. We found a significant enhancement of both IL-13 transcripts and secr eted proteins in the allergen-challenged BAL compared with the saline- challenged control sites of asthmatic and rhinitic patients. In contra st, the expression of IL-13 transcripts was not detected in the BAL of two normal subjects challenged with the same dose of ragweed allergen . The cellular source of IL-13 mRNA was identified in the mononuclear cell fraction of the allergen-challenged BAL. The allergen-induced qua ntitative differences in the level of transcripts were confirmed by co mpetitive PCR assays. These results suggest that the significant incre ase in IL-13 in the allergen-challenged BAL is primarily from the mono nuclear cells and is involved in the regulation of allergen-induced la te phase inflammatory responses.