Studies of allergen-induced airway hyperresponsiveness and inflammation in BLT1-/- mice have shown crucial new roles for LTB4 and BLT1 in Th2 cytokine IL-13 production from lung Th cells, and recruitment of antigen-specific effector CD8+ T cells and CD4+ T cells [37,38], suggesting novel mechanisms for their actions in producing an imbalance in the ratio of Th1/Th2 cytokines, and a possible immune-regulation effect in asthma. This evidence concerns the gene CD4 and airway hyperresponsiveness.