BACKGROUND: Inflammation is a key factor in the pathogenesis of respiratory diseases. Early life exposure to microbial agents may have an effect on the development of the immune system and on respiratory health later in life.In the present work we aimed to evaluate the associations between early life microbial exposures, and fractional exhaled nitric oxide (FeNO) at school age. METHODS: Endotoxin, extracellular polysaccharides (EPS) and β(1,3)-D-glucan were measured in living room dust collected at 2-3 months of age in homes of participants of three prospective European birth cohorts (LISA, n = 182; PIAMA, n = 244; and INMA, n = 355). Home dampness and pet ownership were periodically reported by the parents through questionnaires. FeNO was measured at age 8 for PIAMA and at age 10/11 for LISA and INMA. Cohort-specific associations between the indoor microbial exposures and FeNO were evaluated using multivariable regression analyses. Estimates were combined using random-effects meta-analyses. RESULTS: FeNO at school age was lower in children exposed to endotoxin at age 2-3 months (β -0.05, 95% confidence interval (CI) -0.10;-0.01) and in children with reported dog ownership during the first two years of life (GM ratio 0.82, CI 0.70-0.96). FeNO was not significantly associated with early life exposure to EPS, β(1,3)-D-glucan, indoor dampness and cat ownership. CONCLUSION: Early life exposure to bacterial endotoxin and early life dog ownership are associated with lower FeNO at school age. Further studies are needed to confirm our results and to unravel the underlying mechanisms and possible clinical relevance of this finding.

This work was supported by the European Commission as part of HITEA (Health Effects of Indoor Pollutants: Integrating microbial, toxicological and epidemiological approaches), Grant agreement no. 211488 under the Seventh Framework Programme, Topic ENV.2007.1.2.1.1. “Indoor air pollution in Europe: An emerging environmental health issue”. The LISAplus study was funded by the BMBF (Federal Ministry of Education and Research), the Helmholtz Center Munich and the UFZ Leipzig. The PIAMA study is supported by The Netherlands Organization for Health Research and Development; The Netherlands Organization for Scientific Research; The Netherlands Asthma Fund; The Netherlands Ministry of Spatial Planning, Housing, and the Environment; and The Netherlands Ministry of Health, Welfare, and Sport. The INMA-Menorca study was funded by Fondo de Investigacion Sanitaria, ISCIII, Ministerio de Sanidad y Servicios Sociales, Spain (Grants 97/0588, 00/0021-2, G03/176, PI061756 and PS0901958), EC Contract QLK4-CT-2000-00263 and Fundacio Roger Torne (Barcelona, Spain).