Mast Cells Initiate Type 2 Inflammation through Tryptase Released by MRGPRX2/MRGPRB2 Activation in Atopic Dermatitis

Atopic dermatitis (AD) is a common chronic inflammatory skin disease characterized by T helper 2 inflammation as the core pathogenic mechanism. MRGPRX2 plays a key role in nonhistamine allergies and neuroimmune mechanisms in chronic inflammatory dermatitis. However, the role of MRGPRX2 in AD and the development of type 2 inflammation is not yet clear. This study aimed to define the role of MRGPRX2 in type 2 inflammation development and cytokine release in AD by determining its levels in patients with AD and healthy controls. Furthermore, MrgprB2-conditional knockout (MrgprB2^−/−) and wild-type mice were used to construct an MC903-induced AD mouse model to observe skin inflammation and cytokine release. Tryptase and its antagonist were applied separately to MrgprB2^–/– mice with AD and wild-type mice with AD to confirm the role of the MRGPRB2–tryptase axis in the development of type 2 inflammation in AD. We found that AD severity and type 2 cytokine levels were not associated with IgE levels but were associated with MRGPRX2/MRGPRB2 expression. MrgprB2^–/– mice with AD showed milder phenotypes and inflammatory infiltration in the skin than wild-type mice with AD. Tryptase released by MRGPRX2/MRGPRB2 activation is involved in the release of type 2 cytokines, which contributes to inflammatory development in AD.