IMMUNIZATION WITH THE MAJOR SURFACE GLYCOPROTEIN OF PNEUMOCYSTIS-CARINII ELICITS A PROTECTIVE RESPONSE

Pneumocystis carinii, a leading opportunistic pulmonary pathogen, cont ains a major surface glycoprotein (MSG) which plays a central role in its interaction with the host. Naive Lewis rats were immunized with va rying concentrations of purified native MSG and a recombinant form of the protein (MSG-B), placed in a conventional rat colony with exposure to P. carinii, and immunosuppressed with corticosteroids for 10 weeks to induce the development of pneumocystosis. Immunization elicited hu moral and cellular immune responses to MSG which persisted throughout the experiment. Compared with animals immunized with ovalbumin or adju vant alone, the MSG-immunized rats had improved survival (29 vs 66%, p < 0.001), lowered organism burden (log(10) 9.03 +/- 0.33/lung vs 7.51 +/- 0.38/lung, p < 0.001), less alveolar involvement as assessed by l ung histologic score (3.54 +/- 0.42 vs 2.50 +/- 0.42, p < 0.01) and lu ng weight:body weight ratio (18.2 +/- 1.4 vs 14.6 +/- 1.7, p < 0.01). Animals immunized with MSG-B also showed a significantly lower organis m burden, lung histologic score and lung weight:body weight ratio than control rats. Thus, MSG is the first P. carinii antigen which can eli cit a protective response in the immunosuppressed rat model of pneumoc ystosis and this finding supports the rationale of developing a P. car inii vaccine. (C) 1998 Elsevier Science Ltd. All rights reserved.