Objective:To construct a eukaryotic expression system with pcDNA3-PfCSP/Hela for the Circumsporozoite protein(CSP) gene of Plasmodium falciparum(P.falciparum),to observe the immune responses in BALB/c mice induced by the expressed proteins. Methods:The recombinant plasmid pcDNA3-PfCSP was transformed into the Hela cell line.The expressed protein was isolated and analyzed by using SIDS-PAGE and used for immunization of BALB/c mice by subcutaneous, intravenous, and intraperitoneal adminstration.Enzyme-linked immunosorbent assay(ELISA),Dot-ELISA,Western blot,T lymphocyte proliferation test,natural killer cell(NKC) activity assay,and CD4(+) and CD8(+) T cell detection were used for observation of humoral and cellular immune responses. Results:Immune sera strongly reacted with the expressed protein,antibody titer was up to 1:6400 as detected by ELISA.Western blot analysis revealed a specific band at 38.3 Kda.When the spleen cells of normal and immunized BALB/c mice were specifically stimulated with expressed protein,the optical densities were 0.12+/-0.03 and 0.34+/-0.04,respectively.The latter were significantly higher than the former(P<0.01).We used the MTT colormetric assay to measure NKC activity of mice spleen.The results showed that the NKC activity of immunized BALB/c mice was remarkably higher than that of the controls(P<0.05).CD4(+) and CD8(+) T cells were detected by using monoclonal antibody immunofluorscence methods.The results showed that the percentage of CD4(+) and CD8(+) T cells of immunized group were significantly higher than that of control group(P<0.05).Conclusions:The humoral and cell-mediated immune responses and elevated NKC activity to products made with a eukaryotic expression sytem could be specifically detected in BALB/c mice.These findings indicated that the expressed protein could enhance the immune function in mice. Objective: To construct an eukaryotic expression system with pcDNA3-PfCSP / Hela for the Circumsporozoite protein (CSP) gene of Plasmodium falciparum (P. falciparum), to observe the immune responses in BALB / c mice induced by the expressed proteins. Methods: The The recombinant plasmid pcDNA3-PfCSP was transformed into the Hela cell line. The expressed protein was isolated and analyzed by using SIDS-PAGE and used for immunization of BALB / c mice by subcutaneous, intravenous, and intraperitoneal adminstration. Enzyme-linked immunosorbent assay ), Dot-ELISA, Western blot, T lymphocyte proliferation test, natural killer cell (NKC) activity assay, and CD4 (+) and CD8 (+) T cell detection were used for observation of humoral and cellular immune responses. sera specifically reacted with the expressed protein, antibody titer was up to 1: 6400 as detected by ELISA. Western blot analysis revealed a specific band at 38.3 Kda.When the spleen cells of normal and immunized BALB / c mice were specifically stimulant ted with expressed protein, the optical densities were 0.12 +/- 0.03 and 0.34 +/- 0.04, respectively. These latter were significantly higher than the former (P <0.01) .We used the MTT colormetric assay to measure NKC activity of mice spleen The results showed that the NKC activity of immunized BALB / c mice was remarkably higher than that of the controls (P <0.05) .CD4 (+) and CD8 (+) T cells were detected by using monoclonal antibody immunofluorscence methods.The results showed that the percentage of CD4 (+) and CD8 (+) T cells of immunized group were significantly higher than that of control group (P <0.05) .Conclusions: The humoral and cell-mediated immune responses and elevated NKC activity to products made with an eukaryotic expression sytem could be specifically detected in BALB / c mice. The findings indicate that the expressed protein could enhance the immune function in mice.