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 materials. This gives rise to several problems: variability of allergen composition, contamination with house dust mite allergens, and potential transfer of pathogenic agents.


OBJECTIVE
The aim of this study was to investigate the feasibility of replacing cat epithelial extracts with purified natural or recombinant allergens.


METHODS
Sera (n = 509) were selected on the basis of a positive cat RAST result and tested in a RAST for IgE reactivity to purified Fel d 1, cat albumin (CA), or both. The analysis was performed with both natural and recombinant allergens. In addition, some sera were further analyzed by means of immunoblotting. A serum pool was used for cat RAST inhibition with purified natural 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 sera were low responders to cat extract. The addition of CA (16.7% positive sera) resulted in a decrease in the number of discrepencies between purified allergens and whole extract to 2.8%. Only for 2% of all sera, sensitization to cat was largely explained by IgE reactivity to CA. IgE reactivity to Fel d 1 accounts for 88% of the total IgE response to cat allergens, as was demonstrated by RAST, with Fel d 1 concentrations nearing saturation. Recombinant Fel d 1 performed equally well in the RAST analysis. Recombinant CA was succesfully expressed in the yeast Pichia pastoris, and its immune reactivity closely resembled that of its natural counterpart.


CONCLUSIONS
Natural and recombinant Fel d 1 and CA are good candidates for replacing ill-defined cat dander extracts in diagnostics for cat allergy. Although CA is not essential for the vast majority of cat-sensitized patients, some subjects are selectively sensitized to this serum protein.
van Ree
R
R
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service and the Laboratory for Experimental and Clinical Immunology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
van Leeuwen
W A
WA
Bulder
I
I
Bond
J
J
Aalberse
R C
RC
D000485:Allergens / Q000302:isolation & purification; D000818:Animals; D002415:Cats; D006023:Glycoproteins / Q000302:isolation & purification; D006967:Hypersensitivity / Q000175:diagnosis*; D011852:Radioallergosorbent Test; D011994:Recombinant Proteins / Q000302:isolation & purification; D012709:Serum Albumin / Q000276:immunology* / Q000302:isolation & purification
D000485:Allergens; D006023:Glycoproteins; D011994:Recombinant Proteins; D012709:Serum Albumin; C059296:Fel d 1 protein, Felis domesticus