Immunogenicity evaluation of a recombinant adenovirus containing the PIB and NspA genes of Neisseria gonorrhoeae in mice

Abstract

Objective To evaluate the immunogenicity of a recombinant adenovirus containing the porin IB (PIB) gene and Neisseria surface protein A (NspA) gene of N.gonorrhoeae in BALB/c mice.Methods A recombinant adenovirus containing the PIB gene and NspA gene of N.gonorrhoeae (pAdEasy-1-PN) was constructed in previous studies.Thirty BALB/c mice were randomly and equally divided into 5 groups:low-,medium-and high-dose experiment group intramuscularly immunized with 104,106,and 108 50％ tissue culture infective dose (TCID50) of the recombinant adenovirus pAdEasy-1-PN,respectively,pAdEasy-1 control group immunized with 106 TCID50 of pAdEasy-1,blank control group immunized with sodium chloride physiological solution.Immunization was carried out twice at a 4-week interval.Serum samples were collected at 0,3 and 5 weeks after the first immunization,and spleens were removed at 5 weeks followed by the isolation of spleen lymphocytes.Enzyme linked immunosorbent assay (ELISA) was performed to determine the serum levels of PIB-specific and NspA-specific antibodies,methyl thiazolyl tetrazolium (MTT) assay to evaluate the proliferaton activity of spleen lymphocytes after stimulation by the recombinant PIB and NspA antigens.A slide agglutination test was used to estimate the anti-bacterial activity of murine serum.The complement-dependent bacteriolytic activity of murine serum was also evaluated.Statistical analysis was carried out by t test.Results Both humoral and cellular immune response specific to PIB and NspA were elicited by the recombinant adenovirus in mice.At 3 and 5 weeks after the immunization,significant differences were observed in the serum levels of PIB-specific (F =285.72,564.83,respectively,both P ＜ 0.01) and NspA-specific (F =521.57,542.61,respectively,both P ＜ 0.01)antibodies.Also,the proliferation index was statistically different among these groups in spleen lymphocytes stimulated with PIB and NspA (F =171.61,233.96,respectively,both P ＜ 0.01).The vaccination efficiency was positively correlated with the inoculation dose of recombinant pAdEasy-1-PN,and 108 TCID50 per dose proved to be the optimal dose for immunization.The sera from mice immunized with pAdEasy-1-PN could agglutinate N.gonorrhoeae and kill it in the presence of complement.Conclusions The recombinant adenovirus pAdEasy-1-PN containing PIB and NspA genes could induce specific humoral and cellular immune response in mice,and may be a potential vaccine against N.gonorrhoeae. Key words: Neisseria gonorrhoeae; Adenoviridae; Vaccines,DNA