Reconstituting TLR9 deficient neonates73 with WT bone marrow, or WT neonates with TLR9-deficient bone marrow, should reveal whether TLR9 expression on hematopoietic cells and/or non-hematopoietic cells (such as epithelial cells) plays a role in allergy versus tolerance to food antigens74,75. Here, TLR9 is linked to allergic disease.