PROJECT SUMMARYChildren raised in traditional farm environments rich in microbes are protected from asthma. Our 2016 New EnglJ Med papers characterized the farm effect in two U.S. farming populations the Amish and the Hutterites.Despite similar genetic ancestries and lifestyles Amish and Hutterites follow distinct farming practices (traditionalamong the Amish industrialized among the Hutterites) and show striking disparities in asthma prevalence (4-times lower in the Amish) immune responses and environmental microbial exposures (6.7-fold higher amongthe Amish). Notably inhalation of Amish (but not Hutterite) farm dust extracts (AFDE) dramatically reducedallergen-induced airway hyperresponsiveness (AHR) broncho-alveolar lavage (BAL) eosinophilia and serumIgE and these effects depended on innate immune signaling. These studies showed that the farm environmentprotects from asthma but did not address the mechanisms of protection. Recently we found that the lungs ofAFDE-treated mice (both Balb/c and C57BL/6) harbor a large population of V4+17 T cells (25% of lung Tcells). These cells (which in other models have allergy-suppressive properties) were induced by both autoclavedand non-autoclaved AFDE in Balb/c and C57BL/6 mice of both genders and were invariably present wheneverAFDE inhibited experimental asthma. Lung /V4 transcriptional signatures were robustly associated withinhibition of AHR and BAL eosinophilia and 17 T cells were absent in Myd88/Trif-/- and Hutterite dust extract-treated mice which were not protected from asthma.These preliminary data lead us to hypothesize that lung 17 T cells elicited by AFDE inhalation play a rolein asthma protection. This hypothesis will be tested through complementary in vivo approaches. Aim 1 willdetermine whether T cells (total or 17) are required for the asthma-protective effects of AFDE inhalation.Mice that lack T or 17 T cells because of genetic deficiency (Tcr -/- and Blk-/-) or antibody-mediated depletionwill be assessed for their capacity to be protected from experimental allergic asthma upon AFDE inhalation. Aim2 will determine whether transfers of 17 T cells isolated from the lungs of AFDE-exposed mice are sufficient toprotect unexposed animals from allergic asthma. Total T cells or V4+ 17 T cells isolated from the lungs ofAFDE-treated mice will be adoptively transferred into allergen-treated WT Tcr -/- and Blk-/- (17-deficient) mice.Allergic inflammation phenotypes in recipient mice will be assessed as in Aim 1. The asthma-protective role ofT cell-derived IL17 will also be tested by transferring T cells from Il17a-deficient mice. Aim 3 will characterizecirculating 17 T cells from Amish and Hutterite children for their proportions phenotypes and relation withimmune profiles. Mass cytometry/CyTOF and our previous data on the children's immune profiles will beleveraged to assess whether circulating 17 T cell proportions are higher in school age Amish compared toHutterite children (30 each) and are associated with immune parameters related to asthma protection (e.g. totaland specific IgE neutrophil proportions cytokine levels).