MAPK8 and chronic obstructive pulmonary disease: In addition, to clarify the involvement of MAPK signaling pathways in the expression of IL-33 in HBECs from COPD patients, we examined the effect of MAPK inhibitor, a p38 MAPK inhibitor, SB203580, a JNK inhibitor, SP600125 and an ERK1/2 inhibitor, U0126, on the expression of IL-33 in HBECs from COPD patients.