Colorado PROFILES, The Colorado Clinical and Translational Sciences Institute (CCTSI)
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Study of Allergen, Genetics and Endotoxin (SAGE)

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Thct worldwide prevalence of atopy and asthma is on the rise. Relevant to the induction of atopy and asthma, exposures to antigens, endotoxin and other pathogen-associated molecular patterns (PAMPs) induce both innate and adaptive immune responses. Indeed, co-exposure of potent allergens with biological agents, triggering through receptors of the innate immune system, may be the necessary pathway for adaptive allergic sensitization. These immune responses are controlled both by exposures and genes. In adults, occupational exposures are estimated to contribute 15% of new asthma cases, and occupational asthma serves as an excellent model for the development of adult onset asthma. Research scientists and technicians who work with animals have high rates of symptoms and sensitization to laboratory animals (LA), and are exposed to airborne animal allergens and endotoxin in the workplace. We propose to study this population because it is a model system in which to examine the interaction of exposures, genetics, and the biological mechanisms relevant to allergic sensitization and asthma. We recently demonstrated that endotoxin is the strongest predictor of symptoms to mice, particularly in workers who are not mouse allergic. Endotoxin challenge in volunteers reproduces upper and lower respiratory symptoms reported from occupational exposures. In animals, endotoxin exposure with allergen potentiates allergic sensitization, depending on the timing and dose of endotoxin. Endotoxin may thus act as both a respiratory irritant and as an adjuvant in allergic sensitization. Toll-like receptor 4 (TLR4) and CD14 are two major human endotoxin response elements. Polymorphisms in the human TLR4 coding region and in the CD14 promoter region dictate different functional responses to endotoxin and to allergen, respectively. The TLR4/896G variant reduces human bronchial responsiveness and cytokine release to endotoxin compared to the wild type. The CD14/-159 C variant is associated with markers of allergic disease, although in the context of higher endotoxin exposure, the CD14/-159 T variant is linked to airflow limitation and increased serum IgE. Other, newly described TLR4 and CD14 gene variants may also prove important in these immunologic events, modified by the effect of the other known allergy and asthma genes beta2-adenoreceptor, TNF-alpha, IL-4, IL-4alpha, and IL-13. The central hypothesis of this proposal is that the interaction of endotoxin and allergen with specific host genetic variants of TLR4 and CD14 and other allergy- and asthma-associated genes determines risk for work-related symptoms, airflow limitation, and sensitization to laboratory mice. This hypothesis will be addressed in a cross-sectional study of research scientists, laboratory technicians, and animal handlers, and in a pilot inception cohort longitudinal study of newly hired workers. Sampling for endotoxin and mouse allergen in research laboratories and the animal facility will measure exposure levels for all study subjects, and characterize particle size and distribution. As its primary objective, the proposed study will assess whether the wild type TLR4/896 G variant or the CD14/-156 C or T variant, in combination with airborne endotoxin or mouse allergen, are associated with airflow limitation, symptoms or sensitization to mice. As a secondary objective, the study will assess the contribution of other known asthma and allergy-related gene variants to these health outcomes. A sub-aim will examine the functional significance of gene polymorphisms, by testing in vitro cytokine responses of PBMCs to endotoxin in a nested case control study of subjects categorized by CD14 and TLR4 alleles. As such, the study will determine those exposures and genetic risk factors necessary for symptoms and sensitization to LA, supply information critical for limiting exposures and reducing allergic disease outcomes, and provide broader insight into the process of allergic sensitization and asthma.
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