Betaine supplementation affected single carbon metabolites (A) HYCS, CYSTAT, and METH (not supplemented C57BL/6 black bars, supplemented C57BL/6 vertical striped bars, not supplemented C57Bl/6Mthfr-/- white bars, supplemented C57BL/6Mthfr-/- checkered bars). Betaine supplementation exacerbated the severity of HDM-induced allergic airway disease and abolished the effect of Mthfr loss. (B) Airway hyperresponsiveness (not supplemented HDM-treated C57BL/6Mthfr-/- solid line closed circle, and supplemented C57BL/6Mthfr-/- dashed line open circle and X), and (C) total cells, (D) eosinophils, (E) percentage of eosinophils in WLL. (F) Expression and (G) methylation of Tle4 is altered by betaine supplementation. (* p-value <0.05, ** p-value <0.01 *** p-value <0.001).