Introduction: Dose-response skin prick tests are an important tool to standardise allergen extracts and to evaluate changes in skin test response as a consequence of allergen modifications.

Objectives: To evaluate in vivo and in vitro characteristics of 3 different types of extracts of Phleum pratense, Oleaeuropaea, Parietaria judaica and Dermatophagoides pteronyssinus.

Material and methods: Three types of extracts were used: native unmodified extracts (N), depigmented extracts (DP) (extracts subjected to a mild acid treatment under controlled conditions and dialysis), and a depigmented glutaraldehyde polymerised extract (DPP). Adult patients were skin tested in duplicate with the 3 types of extracts. The dose-response relationship between the geometric mean of the wheal areas and the allergen concentrations was calculated for each patient using regression line analysis. The amount of freeze-dried allergen preparation needed to produce the same wheal size as histamine was calculated in each patient (individual 10 HEP) and for each of the 3 types of extracts. In vitro analysis consisted of major allergen determinations and specific IgE and IgG inhibitions.

Results: The respective 10 HEP values for N, DP and DPP preparations were 0.20 mg, 0.15 and 2.11 for D. pteronyssinus. For P. pratense, these values were 0.02 mg, 0.02 and 0.99; for O. europaea 0.15, 0.44 and 4.9; and for P. judaica 0.01, 0.008 and 1.78 mg.

Conclusions: The polymerised depigmented extracts are significantly less allergenic than the corresponding native and depigmented extracts. This could provide a greater safety margin for the administration of higher doses of immunotherapy in a shorter period of time.

Key words: skin tests, depigmented allergen extracts, glutaraldehyde polymerized allergen extracts, allergoids