Background and Objective The mechanisms operative in specific immunotherapy (SIT) of Type I allergy are not completely understood. In the present study we evaluated immunological changes during SIT in pollinosis.

Method Eight patients suffering from pollinosis (monosensitized to grass pollen) were treated with conventional SIT. All subjects had IgE specific for Phi p 1. a major allergen of timothy grass. In vitro changes in the immunological reactivity to grass pollen extract and to recombinant Phi p 1 were evaluated. Subjects were examined at three occasions: before, after 3 months and after I year of SIT.

Results Serological analysis revealed a marked increase of grass pollen‐ and Phi p 1‐specific IgG, titres of specific IgE did not change significantly. Lymphoproliferative responses to grass pollen extract and rPhl p 1 were reduced already after 3 months of treatment. Accordingly, the cloning efficiency for Ph1 p 1‐specific T‐cell clones (TCC) dropped markedly in all patients. The majority of allergen‐specific TCC raised before SIT revealed a TH₂‐like pattern of cytokine production. TCC established after SIT revealed TH₁ characteristics. This shift was due to a decrease in IL‐4 rather than an increase in IFN‐production by T cells. Investigations of the epitopes recognized by T cells before and after SIT did not reveal the outgrowth of new (ldquo;protecting”) specificities. We could not observe induction of allergen‐speeific CD8⁺ lymphocytes (supressor cells).

Conclusion Our data indicate that — on the level of TH lymphocytes — SIT induces tolerance to the allergen and a modulation of the cytokine pattern produced in response to allergen stimulation.