Abstract: Objective To evaluate immunogenicity of the recombinant protein GST-p55/570 of Pneumocystis carinii. Methods The fusion protein GST-p55/570 was expressed from the prokaryotic expression plasmid pGEX-570, and purified by using glutathione-agarose. The expressed product was analyzed by SDS-PAGE. Thirty-three mice were randomly divided into three groups, immunized with GST-p55/570， GST and PBS, respectively. Each group was immunized for four times at 2 week intervals. At the 7th day after final immunization, spleen was removed to obtain single cell suspension. Proliferation ability of lymphocytes was determined by MTT. Serum samples were collected at pre-immunizaton and two weeks after each immunization. Antibody level in sera of mice was determined by ELISA. The immune response to the recombinant GST-p55/570 recognized by sera of immunized mice was examined by Western blotting. Results The expressed fusion protein GST-p55/570 showed a Mr 47 000. Compared with GST group （1.134 5±0.073 5） or PBS group （1.124 8±0.041 6）, a higher stimulation index （2.063 0±0.160 2） was revealed in GST-p55/570-immunized mice（P＜0.01）. At the 14th to 49th day after immunization, the antibody titer against GST-p55/570 in the immunized group was significantly higher than that of GST or PBS groups （P＜0.01）. Western blotting indicated that the fusion protein （GST-p55/570） had specific immune response to positive serum. Conclusion The fusion protein GST-p55/570 elicits significant humoral and cellular immune responses.

Key words: Pneumocystis carinii, p55 antigen, Immunogenicity