This study shows that when human infant microbiota associated with both AH and prospective allergy was used to colonize GF mice, it resulted in offspring with increased intestinal and systemic Th17 responses, characterized by increased RORγt expression among CD4+ T-cells, and FOXP3−CD4+ T-cells in particular, as well as increased IL-17A secretion. The gene discussed is CD4; the disease is Allergy.