Cellular immune responses induced by DNA vaccine against Chlamydia trachomatis E serotype.

Objective To study cellular immune responses induced by DNA vaccine against Chlamydia trachomatis (Ct) serotype E. Methods BALB/c mice were divided into three groups to be intramuscularly immunized by blank plasmid (negative control group), DNA vaccine against Ct serotype E (vaccine group), and inactivated Ct elementary body (positive control group), respectively. Two weeks after the last immunization,delayed-type hypersensitivity (DTH) response was evaluated; MTT assay was performed to detect the proliferation of spleen lymphocytes, ELISA to measure the serum level of interferon-γin mice. Some immunized mice underwent a genital challenge with Ct elementary body followed by isolation of Ct from exfoliated epithelial cells in genital tract and pathological examination of cervical tissue from the challenged mice. Results Compared to negative control group, vaccine group and positive control group experienced a stronger DTH response.The lymphocyte stimulating index and serum level of IFN-γwere highest in the positive control group (3.81 ±0.30, 2891.7 ± 1048.8 μg/L), followed by vaccine group (2.35 ± 0.25, 593.3 ± 342.6 μg/L) and negative control group (1.48 ± 0.15, 309.2 ± 157.9 μg/L), and significant difference was observed between the three groups (P ＜ 0.05 or 0.01 ). After Ct challenge, Ct was isolated from exfoliated epithelial cells and cervical tissue was damaged in the negative control group, while in the other two groups, Ct was undetected and genital tract tissue was intact. Conclusions The DNA vaccine against Ct serotype E could induce Ct-specific cellular immune responses to some extent, and offer a protection against vaginal challenge with Ct. Key words: Chlamydia trachomatis;  Vaccines, DNA;  Immunity, cellular;  Hypersensitivity, delayed