ADRB2 and asthma: These combined findings were supported by a recent study in which a variant of ADCYAP1R1 in combination with extrinsic stress led to reduced BDR in children with asthma and reduced levels of ADRB2 in CD4 + T cells (Brehm et al., 2015); the CD4+ cell type has been shown to have a significant role in an asthmatic response (Ling and Luster, 2016).