OBJECTIVE: To probe into the role of vitamin D（VitD） in improving chronic rhinosinusitis（CRS） model induced by Streptococcus pneumoniae by regulating the imbalance of T regulatory cells/T helper 17 cells（Treg/Th17） cell function. METHODS: Totally 40 male C57BL/6 mice were divided into the control group（Control）

model group（Model）

VitD group（VitD） and clarithromycin group（CLR） according to the random table method

with 10 mice in each group. Except for the control group

the other groups were filled with sponges containing S. pneumoniae in the sinus cavity to replicate the CRS model. The VitD group and CLR group were administered with VitD

3

solution and clarithromycin solution by gavage respectively. After 21 d

the levels of interleukin（IL）-6

IL-10

IL-17

IL-23 and transforming growth factor-β（TGF-β） in the serum of mice were detected by enzyme linked immunosorbent assay. Hematoxylin and Eeosin staining and periodic acid-schiff staining were used to observe the pathological changes of mucous membranes of the nasal sinuses of mice

real-time quantitative polymerase chain reaction and Western blotting were used to detect the mRNA and protein expression levels of retinoic acid-related orphan receptor γt（RORγt） and forkhead family transcription factor 3（Foxp3） in the mucous membranes of the nasal sinuses of mice

immunohistochemical staining was used to detect the positive expression of IL-17 and Foxp3 in the sinus mucosa of mice

and flow cytometry was used to analyze the distribution of CD4

+

IL-17A

+

and CD25

+

Foxp3

+

cells in peripheral blood. RESULTS: Compared with the control group

the serum levels of IL-6

IL-17 and IL-23 in the model group increased

while the levels of IL-10 and TGF-β decreased（P

<

0.05）; obvioued lesions occurred in the sinus mucosa

with a large number of inflammatory cells infiltrating

the number of goblet cells increased（P

<

0.05）; the relative expression of RORγt mRNA and protein was up-regulated

and the relative expression of Foxp3 mRNA and protein was down-regulated（P

<

0.05）; the positive expression rate of IL-17 increased

while the positive expression rate of Foxp3 decreased（P

<

0.05）

the proportion of CD4

+

IL-17A

+

cells in peripheral blood increased

and the proportion of CD25

+

Foxp3

+

cells decreased（P

<

0.05）

with statistically significant differences. Compared with the model group

the serum levels of IL-6

IL-17 and IL-23 in the VitD group and CLR group decreased

while the levels of IL-10 and TGF-β increased（P

<

0.05）; the infiltration was alleviated

and the number of goblet cells decreased（P

<

0.05）; at the same time

the relative expressions of RORγt mRNA and protein were down-regulated

the relative expressions of Foxp3 mRNA and protein were up-regulated（P

<

0.05）

the positive expression rate of IL-17 decreased and the positive expression rate of Foxp3 increased（P

<

0.05）

the proportion of CD4

+

IL-17A

+

cells in peripheral blood decreased and the proportion of CD25

+

Foxp3

+

cells increased（P

<

0.05）

with statistically significant differences. CONCLUSIONS: VitD can improve the pathological manifestations of sinus mucosa in CRS model mice and reduce inflammatory cell infiltration

and its mechanism may be related to the regulation of imbalance of Treg/Th17 cell function.