Timothy grass pollen allergen (specific canonical forms: Phl p 1, Phl p 2, Phl p 5, Phl p 12; collectively referred here as Timothy grass pollen allergen for generic use) (Phl p (Phl p 1, Phl p 2, Phl p 5, Phl p 12; specific to isoallergen if required))

Timothy grass pollen allergen refers to a group of proteins from the pollen of *Phleum pratense*, most notably Phl p 1, Phl p 2, and Phl p 5, which are the major elicitors of allergic rhinitis and asthma in sensitized individuals[1][2][5]. Phl p 1 (beta-expansin) and Phl p 5 are especially significant, with upward of 90% of grass pollen allergic individuals producing IgE antibodies to these antigens[5][1][3]. These proteins belong to various structural families: Phl p 1 is a beta-expansin, Phl p 5 comprises two main isoforms (5a, 5b) with possible ribonuclease activity, and Phl p 2 is structurally unique as a non-glycosylated protein, while Phl p 12 is a profilin[5][1][3]. All are potent activators of type I hypersensitivity and can cross-react with other grass pollens or even plant foods, contributing to the pollen-food syndrome. In clinical practice, these allergens are both the key antigens for allergy testing and targets for specific immunotherapy (allergy desensitization), but the main therapeutic focus is modulation of the immune response rather than direct inhibition of the allergen protein itself[5][2][3].

Other names

Group 1 grass pollen allergen (Phl p 1)Group 2 grass pollen allergen (Phl p 2)Group 5 grass pollen allergen (Phl p 5, includes Phl p 5a, Phl p 5b)Timothy grass (Phleum pratense) pollen allergenAg25 (for Phl p 5)Phl p Vb (for Phl p 5b)

Induction of IgE-mediated immune reactions in sensitized individuals; Binds to IgE on mast cells/basophils, cross-linking leads to degranulation and release of histamine; Drugs in immunotherapy induce tolerogenic immune responses by repeated exposure to allergen protein