The present invention relates to a method of treating Pneumocystis pneumonia infection in a subject. This method involves administering to a subject having a Pneumocystis pneumonia infection one or more antibodies that bind specifically to a Pneumocystis cross-reactive antigen 1 (PCA1) protein under conditions effective to treat the Pneumocystis infection in the subject. Another aspect of the present invention relates to a method of treating a subject at risk for Pneumocystis pneumonia infection. A further aspect of the present invention relates to an isolated protein or polypeptide comprising the amino acid sequence of SEQ ID NO:1. Another aspect of the present invention relates to a pharmaceutical composition comprising the isolated protein or polypeptide of the present invention and a pharmaceutically acceptable carrier.
