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Stability of Pityrosporum ovale allergens during storage
P Lintu1, J Savolainen, K Kalimo
1Department of Pulmonary Diseases and Clinical Allergology, University of Turku, Finland.
Background:
Pityrosporum ovale is a common saprophyte on the skin capable to induce IgE antibody production in atopic dermatitis. Generally IgE response to P. ovale has been established with skin-prick test, but the stability of P. ovale skin test allergens is not known.
Objective And Methods:
In this study we analysed the stability of identified allergens of P. ovale in skin test solutions during storage. The stability was checked with immunoblotting and densitometry after different time periods and at various temperatures.
Results:
Coomassie Brilliant blue staining clearly showed, that proteins were preserved poorly at + 20 degrees C in 50% glycerol. Even extracts stored at + 4 degrees C during 6 and 12 months in 50% glycerol were degraded. Only extract stored at + 4 degrees C for 1 month in 50% glycerol was quite well preserved. According to densitometry results the 9 kDa band was the most stable main protein allergen. The 20 kDa and especially the 96 kDa bands were far more labile. The stability of low molecular allergens was in general better than the stability of high molecular weight allergens.
Conclusions:
The stability of P. ovale extracts stored for more than 1 month was poor even when kept at + 4 degrees C temperature. Reliability of negative skin prick results should be questioned when older extracts are used. In skin test negative cases, the sensitization should be evaluated also with the measurement of specific serum IgE antibodies to P. ovale.