Conclusion
The high levels of SP-D, KL-6, and HTI-56 in infected bronchoalveolar lavage fluid samples may reflect the injury of alveolar epithelium caused by M. pneumoniae. Instead of SP-D in uninfected bronchoalveolar lavage fluid samples obtained by invasive bronchoscopy, serum SP-D may serve as a convenient medium to distinguish lung infection caused by M. pneumoniae.