Cross-reactivity in Grasses: Biochemical Attributes Define Exemplar Relevance

INTRODUCTION: Broad-spectrum grass pollen immunotherapies contain large numbers of allergenic proteins from multiple species. The principle of homologous grouping is used as a tool to assist in the standardization of allergen immunotherapy. This study reviews the principle of homologous grouping, questions what an exemplar grass should be, and queries whether a 1-way system of inferring homology is appropriate. METHODS: Grass pollens were extracted and analyzed using a variety of techniques, including enzyme-linked immunosorbent assay, Bradford protein assay, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and quantitative analysis of Western blots. RESULTS: Variation in protein content, IgG, IgE, and Phl p 5 reactivity is evident among all grasses analyzed. There is significant evidence of similarity but also disparity consistent with variation resulting from evolutionary change. Proprietary software called Gel Electrophoresis Protein Profile Analysis has been developed, which highlights that each grass exhibits a greater than 55% similarity measure; this is considered high similarity. DISCUSSION: None of the grass species examined display an identical biological profile. However, data indicate that there is a high degree of homology, and Crested Dogstail is similar to each of the other 12 species analyzed; these levels of similarity can only be possible because of molecular profile and extensive sharing of epitopes. These data are considered to be sufficient to include Crested Dogstail within the sweet grasses group of the Pooideae family; however, the subtle differences in grasses also justify the inclusion of multiple species to create a broad-spectrum immunotherapy.