Objective To evaluate the effects of recombinant fusion protein interleukin-17F/His (IL-17F/His) on expression of immune-related inflammatory factors in murine models with Streptococcus pneumoniae (SP) infection. Methods BALB/c mice were randomly divided into SP infection group, fusion protein intervention group and the normal control group.Before intranasal infection with SP, the mice were treated with PBS or IL-17F/His respectively.The number of bacteria and leukocytes in bronchoalveolar lavage fluid (BALF) was counted, and the mRNA levels of β-defensin-2 (Defb2), macrophage inflammatory protein (MIP)-1α and MIP-2β in lung tissue were detected by real-time fluorescent quantitative PCR, the concentrations of MIP-1α, MIP-2β, IFN-γ and IL-4 in BALF, supernatants of spleen cell and mediastinal lymph node cell were assayed by enzyme linked immunosorbent assay.The expressions of IL-17F and Defb2 in lung tissues were observed with immunocytochemistry. Results 1.Compared with the SP infection group, in the fusion protein intervention group, the total number of WBC (209.00±18.23)was higher, the number of neutrophil, macrophage and lymphocyte[(8.67±2.16)×106/L, (193.50±16.50)×106/L, (6.83±1.17)×106/L]were higher in BALF(U/F=38.097, 28.854, 32.942, 27.810, all P<0.05), while the number of bacteria[2.75(1.15-3.09)×103/L]was significantly lower(P=0.02).2.Compared with SP infection group, the expression levels of Defb2 mRNA and MIP-1α mRNA(31.64±4.97, 5.81±1.09) in lung tissues were higher in the fusion protein intervention group, while the expression level of MIP-2β mRNA(6.69±2.05) was lower(t=4.889, 2.306, 3.536, all P<0.05).3.Compared with the SP infection group, the concentration of MIP-2β[(64.15±13.41) ng/L] was significantly decreased and concentration of IL-4[(92.28±4.52) ng/L]was significantly increased in BALF in the fusion protein intervention group(H/F=159, 289, 40.767, all P<0.01).4.Compared with the SP infection group, the concentrations of MIP-2β and IL-4[(255.02±13.95) ng/L, (107.02±7.53) ng/L] were both significantly increased in spleen cell culture supernatants in the fusion protein intervention group, the concentrations of MIP-1α and IFN-γ[(413.61±24.23) ng/L, (98.88±5.84) ng/L]were both significantly decreased(all P<0.05).5.Immunocytochemistry analysis revealed that the expressions of IL-17F and Defb2 were both higher in the fusion protein intervention group than those in the SP infection group; there was no expression in the normal control group. Conclusions Intranasal inoculation of recombinant fusion protein IL-17F/His can promote pulmonary neutrophil and macrophage recruitment and increase bacterium clearance, and enhance the host defense against SP infection through increa-sing the expression of defensins, regulating the levels of MIP, IL-4 and IFN-γ. Key words: Interleukin-17F; Streptococcus pneumoniae infection; β-defensin-2; Macrophage inflammatory protein