ABSTRACT
Our previous study showed that recombinant canine IL-13 (rcaIL-13) stimulated production of allergen-specific IgE in vitro by peripheral blood mononuclear cells (PBMC) from flea allergen-sensitized dogs. This has also been demonstrated using human IL-13 (huIL-13) and PBMC isolated from human allergy patients. The stimulatory activity of rcaIL-13 was specifically inhibited by a fusion protein of the extracellular domain of canine IL-13Ralpha2 and the Fc fragment of canine IgG heavy chain (rcaIL-13Ralpha2-Fc). In this communication, we report the construction and expression of a non-fused recombinant extracellular domain of canine IL-13Ralpha2 (rcaIL-13Ralpha2) in an E. coli expression system. The E. coli expressed rcaIL-13Ralpha2 was isolated in inclusion bodies, then solubilized in buffer containing denaturants and reducing agents. After refolding and purification, the biological activity of rcaIL-13Ralpha2 was found in the monomer fraction resulting from gel filtration and ion exchange chromatographies. Biological activity of purified rcaIL-13Ralpha2 was demonstrated by the specific inhibition of rcaIL-13 activity in a TF-1 cell proliferation assay. Additionally, rcaIL-13Ralpha2 was found to be active in neutralizing rcaIL-13 induced upregulation of IgE mRNA levels in PBMCs of "high IgE" dogs, which have been bred to exhibit a predisposition for high IgE production and are used as a model for allergic asthma. The data confirm our previous report that the regulatory effects of IL-13 on IgE production in canine PBMCs are similar to those reported in humans. Thus, allergic dogs, such as the "high IgE" producing dogs, may be excellent models for research on IgE-mediated diseases in humans.