Mapping of T-cell epitopes of Phl p 5: evidence for crossreacting and non-crossreacting T-cell epitopes within Phl p 5 isoallergens

Background Group 5 allergens represent major grass pollen allergens because of their high sensitization indices. The identification of T-cell epitopes of these allergens is a prerequisite for the design of immunotherapeutic s trategies based on peptide vaccination or modified allergens with conserved T-cell epitopes. Objective This study was undertaken to determine T-cell epitopes on Phl p 5 major pollen allergen of timothy grass (Phleum pratense). Methods T-cell lines (TCLs) and T-cell. clones (TCCs), specific to Phl p 5, were established from the peripheral blood of 18 patients allergic to gras s pollen. All TCCs were mapped for epitope specificities using 178 overlapp ing dodecapeptides representing the primary structures of two isoforms of P hl p 5 (Phl p 5a and Phl p 5b). Phenotype and cytokine production profiles of TCCs were tested. Selected TCCs were analysed for HLA class II restricti on. Results A total of 82 TCCs were isolated. All TCCs displayed the helper cel l (TH) phenotype. Their reactivity with two recombinant expressed isoforms of Phl p 5a and Phl p 5b was heterogeneous. The epitope specificity of the TCCs was then revealed. Nineteen T-cell epitopes could be identified on Phl p 5. Eighty-one percent of mapped TCCs recognized three T-cell reactive re gions on the Phl p 5 allergen. Some TCCs were reactive with isoepitopes pre senting on Phl p 5a as well as Phl p 5b. Allergen-specific stimulation indu ced a TH0-like type of cytokine production in 25 of 50 TCCs. Almost all TCC s secreted high concentrations of interleukin-13. Conclusion Phl p 5, a major grass pollen allergen, contains several T-cell epitopes. Some epitope regions were recognized by several patients. Epitope recognition pattern could not be correlated with special HLA class II hapl otypes. T-cell stimulating isoepitopes were found at corresponding regions of Phl p 5a and Phl p 5b isoforms.