A large panel of T cell clones (TCC) specific for the recombinant form of Poa pratensis allergen (rKBG7.2 or Poa p9) were established from the peripheral blood of grass pollen-sensitive donor in the absence or presence of recombinant interferon-alpha (IFN-alpha) in bulk culture and their pattern of cytokine secretion, peptide reactivity and TCR V beta repertoire was examined. The majority of allergen-specific TCC derived in absence of IFN-alpha produced high amounts of interleukin-4 (IL-4) and IL-5 but not IFN-gamma (Th2 cells), while most of TCC derived in presence of IFN-alpha produced IFN-gamma but not, or limited amounts of, IL-4 and IL-5 (Th1 or Th0 cells). Of 24 TCC established in the presence of IFN-alpha, 22 were able to recognize a single allergen peptide, p26, while none of the clones established in the absence of IFN-alpha showed a similar specificity. The majority of both clones expressed the V beta 2 element regardless of whether they were established in the presence of INF-alpha, but the presence of IFN-alpha favored the expansion of V beta 2+, V beta 17+ and V beta 22+ Poa p9-specific T cells, whereas in the absence of IFN-alpha, other TCR V beta-bearing T cells (V beta 5, and V beta 6.7, and V beta 14) were expanded in addition to V beta 2+ T cells. None of V beta 2+ clones established in the absence of IFN-alpha reacted with p26, whereas all the V beta 2+ clones established in its presence in the absence of interferon-alpha reacted with p26, whereas all the V beta 2+ clones established in its presence reacted to this peptide. IFN-alpha also shifted the TCR V beta repertoire of both Poa p9- and Lolium perenne group 1 (Lol p1)-specific T cell lines generated from the same patient and from a different grass-sensitive individual. These data demonstrate that IFN-alpha modulates the development of allergen-specific T cells in vitro, and suggest that IFN-alpha may represent a useful tool for novel immunotherapeutic approaches in allergic disorders.