Okamoto, Tsukasa, et al. “Seasonal Variation of Serum KL-6 and SP-D Levels in Bird-Related Hypersensitivity Pneumonitis”.
Sarcoidosis, Vasculitis and Diffuse Lung Diseases, vol. 31, no. 4, Jan. 2015, pp. 364-7,
https://mattioli1885journals.com/index.php/sarcoidosis/article/view/3525.