Grass pollen Group 1 and Group 5 allergens (Group 1/5 grass allergens)

Grass pollen Group 1 and Group 5 allergens are the primary proteins responsible for seasonal allergic rhinitis and asthma in individuals sensitized to grasses of the Poaceae family. Group 1 allergens, such as Phl p 1 from Timothy grass, are beta-expansins that facilitate pollen tube penetration by loosening plant cell walls during fertilization [Cosgrove, 2000]. Group 5 allergens, such as Phl p 5, are highly potent proteins found in the pollen cytosol whose exact biological function in the plant remains less defined, though they exhibit high IgE-binding frequency in allergic patients [Bufe et al., 1995]. In the human immune system, these allergens cross-link IgE antibodies on the surface of mast cells and basophils, triggering the release of inflammatory mediators like histamine. These allergens serve as the active pharmaceutical ingredients in allergen-specific immunotherapy (AIT) products, such as sublingual tablets (e.g., Grastek, Oralair) and subcutaneous injections. The therapeutic goal is to desensitize the patient's immune system through controlled, escalating exposure to the allergens. This process induces the expansion of regulatory T and B cells and the production of protective IgG4 antibodies, which compete with IgE for allergen binding. Clinical efficacy is typically monitored through symptom scores and the measurement of specific antibody ratios in the serum [WHO/IUIS Allergen Nomenclature, 2024].

Other names

Phl p 1Phl p 5Lol p 1Lol p 5Beta-expansinGrass pollen isoallergensMajor grass pollen allergens

Allergen-specific immunotherapy (AIT) involves the repeated administration of these allergens to induce immunological tolerance. This is achieved by shifting the immune response from a Th2-dominated profile to a Th1 and Regulatory T-cell (Treg) response, leading to the production of allergen-specific IgG4 blocking antibodies that prevent IgE-mediated mast cell degranulation [Durham & Shamji, 2023; Valenta et al., 2019].