Scirpus planiculmis Extract Inhibits the Activation of Syk to Suppress Mast Cell-mediated Allergic Responses in vitro and in vivo

Scirpus planiculmis (SP) has been used for a long time as a traditional therapy to cure bronchiectasis, gynecopathy, chest pain, and dyspepsia in Asian countries. However, the therapeutic effect of SP on allergic diseases remains to be determined. In this study, we observed the anti-allergic effect and its mechanism of SP in mast cells and mice. SP significantly suppressed the degranulation and expression of tumor necrosis factor-α (TNF-α) and interleukin-4 (IL-4) in mast cells stimulated by antigen, and its inhibition was reversible. Mechanistically, SP inhibited the activation of spleen tyrosine kinase (Syk) by antigen and its downstream signaling proteins such as linker for activation of T cell (LAT), phospholipase Cγ (PLCγ), Akt, and mitogen activated protein (MAP) kinases, including ERK, JNK, and p38, in a dose-dependent manner. In mice, SP significantly inhibited the passive cutaneous anaphylaxis (PCA) reaction and degranulation of mast cells in ear tissue by antigen. Taken together, SP suppressed the allergic response by antigen in mice via the inhibition of Syk activation in mast cells, which warrants further investigation for developing anti-allergic herbal medicine.