Purified natural and recombinant Fel d 1 and cat albumin in in vitro diagnostics for cat allergy

Background: Current diagnostics and therapeutics for cat allergy are based on cat epithelial extracts originating from highly variable source material s, This gives rise to several problems: variability of allergen composition , contamination with house dust mite allergens, and potential transfer of p athogenic agents. Objective: The aim of this study was to investigate the feasibility of repl acing cat epithelial extracts with purified natural or recombinant allergen s. Methods: Sera (n = 509) were selected on the basis of a positive cat RAST r esult and tested in a RAST for IgE reactivity to purified Fel d 1, cat albu min (CA), or both. The analysis was performed with both natural and recombi nant allergens, In addition, some sera were further analyzed by means of im munoblotting, A serum pool was used for cat RAST inhibition with purified n atural and recombinant allergens as inhibitors. Results: Natural and recombinant Fel d 1 caused very similar results: 94.1% and 96.1% positive test results, respectively. In general, the negative se ra were low responders to cat extract. The addition of CA (16.7% positive s era) resulted in a decrease in the number of discrepencies between purified allergens and whole extract to 2.8%. Only for 2% of all sera, sensitizatio n to cat was largely explained by IgE reactivity to CA. IgE reactivity to F el d 1 accounts for 886 of the total IgE response to cat allergens, as was demonstrated by RAST, with Fel d 1 concentrations nearing saturation, Recom binant Fel d 1 performed equally well in the RAST analysis. Recombinant CA was succesfully expressed in the yeast Pichia pastoris, and its immune reac tivity closely resembled that of its natural counterpart. Conclusion: Natural and recombinant Fel d 1 and CA are good candidates for replacing ill-defined cat dander extracts in diagnostics for cat allergy, A lthough CA is not essential for the vast majority of cat-sensitized patient s, some subjects are selectively sensitized to this serum protein.