AUTHOR=Frew John W. TITLE=The Hygiene Hypothesis, Old Friends, and New Genes JOURNAL=Frontiers in Immunology VOLUME=10 YEAR=2019 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.00388 DOI=10.3389/fimmu.2019.00388 ISSN=1664-3224