The biological potency of different extracts for sublingual immunotherapy assessed by skin prick tests

The standardization of allergen extracts is of primary relevance to the clinical efficacy. Biological standardization procedures are widely used in the commercial production of vaccines. We tested, in grass-allergic patients, the potency of three different grass extracts for sublingual immunotherapy by means of skin prick tests. Specific IgE against Phl p 1, 2, 4, 5, 7, 11 and 12 were also assayed. Allerslit and Sublivac were directly applied as skin test. Grazax, was prepared by dissolving two tablets in 2 mL saline. Thirty-three subjects (mean age 38.8) were studied. The skin response was significantly different among extracts, decreasing from Allerslit to Grazax (t test < 0.01), but all the extract produced a skin response greater than histamine. All the subjects had specific IgE to Phl p 1 and Phl p 4 but 24% did not have specific IgE to Phl p 5. In those subjects the skin response to the three extracts did not differ from that of Phl p 5-positive subjects. Our findings confirm that there is a variability in the biological potency among different extracts. In addition, the standardization of grass extracts based on Phlp 5 only, may be insufficient in some cases.