1 362 139 AMBIENT AIR POLLUTION IMPAIRS REGULATORY T-CELL FUNCTION IN ASTHMA. BACKGROUND: ASTHMA IS THE MOST FREQUENT CHRONIC DISEASE IN CHILDREN, AND CHILDREN ARE AT HIGH RISK FOR ADVERSE HEALTH CONSEQUENCES ASSOCIATED WITH AMBIENT AIR POLLUTION (AAP) EXPOSURE. REGULATORY T (TREG) CELLS ARE SUPPRESSORS OF IMMUNE RESPONSES INVOLVED IN ASTHMA PATHOGENESIS. TREG-CELL IMPAIRMENT IS ASSOCIATED WITH INCREASED DNA METHYLATION OF FORKHEAD BOX TRANSCRIPTION FACTOR 3 (FOXP3), A KEY TRANSCRIPTION FACTOR IN TREG-CELL ACTIVITY. BECAUSE AAP EXPOSURE CAN INDUCE EPIGENETIC CHANGES, WE HYPOTHESIZED THAT TREG-CELL FUNCTION WOULD BE IMPAIRED BY AAP, ALLOWING AMPLIFICATION OF AN INFLAMMATORY RESPONSE. OBJECTIVES: TO ASSESS WHETHER EXPOSURE TO AAP LED TO HYPERMETHYLATION OF THE FOXP3 GENE, CAUSING IMPAIRED TREG-CELL SUPPRESSION AND WORSENED ASTHMA SYMPTOM SCORES. METHODS: CHILDREN WITH AND WITHOUT ASTHMA FROM FRESNO, CALIF (HIGH POLLUTION, FRESNO ASTHMA GROUP [FA], N = 71, AND FRESNO NON ASTHMATIC GROUP, N = 30, RESPECTIVELY), AND FROM STANFORD, CALIF (LOW POLLUTION, STANFORD ASTHMA GROUP, N = 40, AND STANFORD NON ASTHMATIC GROUP, N = 40), WERE ENROLLED IN A CROSS-SECTIONAL STUDY. PERIPHERAL BLOOD TREG CELLS WERE USED IN FUNCTIONAL AND EPIGENETIC STUDIES. ASTHMA OUTCOMES WERE ASSESSED BY GLOBAL INITIATIVE IN ASTHMA SCORE. RESULTS: FRESNO ASTHMA GROUP TREG-CELL SUPPRESSION WAS IMPAIRED AND FA TREG-CELL CHEMOTAXIS WERE REDUCED COMPARED WITH OTHER GROUPS (P