Pneumocystis jiroveciiis the most common cause of fungal pneumonia in children under the age of 2 years. However, the inability to culture and propagate this organism has hampered the acquisition of a fungal genome as well as the development of recombinant antigens to conduct seroprevalence studies. In this study, we performed proteomics onPneumocystis-infected mice and used the recentP. murinaandP. jiroveciigenomes to prioritize antigens for recombinant protein expression. We focused on a fungal glucanase due to its conservation among fungal species. We found evidence of maternal IgG to this antigen, followed by a nadir in pediatric samples between 1 and 3 months of age, followed by an increase in prevalence over time consistent with the known epidemiology ofPneumocystisexposure. Moreover, there was a strong concordance of anti-glucanase responses and IgG against anotherPneumocystisantigen, PNEG_01454. Taken together, these antigens may be useful tools forPneumocystisseroprevalence and seroconversion studies.