Pollen is a ubiquitous allergen that affects a large population with allergic diseases. However, the mechanisms leading to resolution of pollen allergen-induced inflammation remain poorly understood, a knowledge gap preventing us from developing new targeted therapies to cure allergic diseases. We have recently uncovered a novel pollen/TLR4 innate immunity pathway where short ragweed (SRW) pollen triggers allergic inflammation via TLR4-dependent innate signaling by mucosal epithelium that produces proallergic cytokine thymic stromal lymphopoietin (TSLP). We thus extended our investigation to another epithelial proallergic cytokine interleukine (IL) 33 and other major innate immune cells that may respond to pollen allergen. We hypothesize that TLR4-dependent innate immunity by ocular mucosal epithelia, dendritic cells and macrophages in response to pollen allergen, initiates Th2-dominant allergic inflammation via two stimulated allergic pathways, TSLP/OX40L/OX40 and IL-33/ST2, with an inhibited protective signaling IL-27/IL-10. The long-term goal of this project is to discover new molecular mechanisms and novel therapeutic targets for treating allergic diseases. Four Specific Aims are proposed to fulfill this novel project for public health. Aim 1 is to confirm the hypothesis that SRW pollen stimulates production of two pro-allergic cytokines TSLP and IL-33 by ocular epithelium via activating TLR4/MyD88/NF-?B innate immunity pathway; Aim 2 is to investigate the hypothesis that TLR4-dependent innate immune responses by dendritic cells amplify Th2-dominant inflammation via autocrine activation of TSLP/OX40L and IL-33/ST2 signaling with inhibitory regulation of IL-27 in response to SRW pollen allergen; Aim 3 is to explore the hypothesis that SRW pollen allergen primes macrophage polarization toward an alternatively activated (M2) phenotype to promote Th2- inducing cytokines (TSLP, IL-33 and OX40L) and Th2-attracting chemokines (CCL17 and CCL22) via TLR4-dependent innate immunity; and Aim 4 is to test the hypothesis that pollen/TLR4 concept may create a novel TLR4-targeted therapy for pollen-triggered allergic diseases using TLR4 antagonists and/or agonists. At the conclusion of this project, we will uncover a novel phenomenon and molecular mechanism by which pollen allergen triggers Th2-dominant allergic inflammation via TLR4-dependent innate immune response that activates TSLP/OX40L/OX40 and IL-33/ST2 allergic pathways but suppresses IL-27/IL-10 protective signaling in mucosal innate immunity system. The end product of this project will be a fundamental new understanding and potential TLR4-targeted therapeutic strategies, a new hope to prevent and cure allergic disease.