[Acquisition and the immunogenicity of the outer membrane FomA protein of Fusobacterium nucleatum]

Objective: To express and purify outer membrane protein FomA of Fusobacterium nucleatum (Fn) through gene recombination technique with Escherichia coli (Ec) expression system, and to detect the immunogenicity and the immune effects of the recombinant protein on gingival tissues. Methods: The gene recombination technique and Ec expression system were used to express and purified the FomA protein. Totally 20 C57 mice were immuned with the protein or the phosphate buffer solution (PBS) buffer by subcutaneous injection (each 10 mice), and the specific FomA antibody was detection in mice serum. The immunogenicity of FomA protein was assessed by comparing the differences between groups. Furthermore, the model of mice gum abscess was constructed with Fn or Fn and Porphyromonas gingivalis (Pg) mixed suspension used the above mice. The score of the gingival abscess was recorded and the interleukin (IL)-1β in gum tissue and mice serum was determined by enzyme-linked immunosorbent assay method, and the differences of the indexes between groups were compared to evaluate the effect of the FomA protein immunization. Results: Totally 1.0-1.5 g FomA protein were successfully obtained and the protein purity was over 90%. The FomA specific antibody was detected in the serum of mice by subcutaneous injection of the protein, and the antibody titer reached the highest level in 2 weeks after secondary immunization. The model of submaxillary gingival abscess was successfully constructed. In the Fn model, the score of the FomA protein immune group was (1.82±0.35), and the PBS control group was (2.62±0.71), with statistically significant difference between the two groups (P=0.049). In the Fn+Pg mixture model, the score of gingival abscess in the FomA immune group (2.31±0.55) was lower than that in PBS group (3.63±0.45), and the difference was statistically significant (P=0.003). Both in Fn and Fn+Pg injection group, the concentration of IL-1β in the serum of FomA immune mice and gingival tissues was lower than that of PBS control mice (P<0.001). Conclusions: The recombinant FomA protein can be acquired by Ec expression system, and it can produce a certain level antibodies in the mice serum. The way of mice subcutaneously injected with the recombinant FomA protein can reduce the severity of periodontal infections caused by Fn and Pg.