The protein expression levels of IL-5 [41.99 (21.11)], IL-9 [27.04 (37.51)], IL-13 [184.05 (132.81)], IL-33 [83.70 (46.69)], and TSLP [31.42 (5.41)] in peripheral blood of the bronchiolitis group were higher than those [25.70 (19.64), 8.30 (0.54), 121.75 (176.13), 11.23 (55.31), and 28.76 (2.56) respectively] in the control group, and the differences between the two groups were statistically significant (P < 0.05, see Figs. 4, 5 and 6). Here, IL9 is linked to bronchiolitis.