TLR4 and respiratory syncytial virus bronchiolitis: A gene-environment interaction as documented between toll like receptor 4 (TLR4) D299G single nucleotide polymorphism and environmental endotoxin exposure reveals a possible T helper 2 (Th2) polarizations in patients with severe RSV bronchiolitis, which may become useful for early identification of these patients at risk of severe RSV disease (9).