AHR and allergic asthma: Different dendritic cell subsets can dictate the allergic immune response and targeting either dendritic cell activation or molecules involved in antigen presentation may be a fruitful approach to therapeutically target allergic asthma, and specifically different immune phenotypes of disease.54,55 PD-L1 is known to enhance AHR and Th2 cytokine production in allergic mice.56 Therefore, a reduction in PD-1–PD-L1 signaling, alongside reduced OX40 signaling, may explain the reduced Th2 response in C57BL/6 mice compared with BALB/c.