Open Access Research article

The elevation of serum napsin A in idiopathic pulmonary fibrosis, compared with KL-6, surfactant protein-A and surfactant protein-D

Takuya Samukawa1, Tsutomu Hamada1, Hirofumi Uto2, Masakazu Yanagi3, Go Tsukuya1, Tsuyoshi Nosaki2, Masahiro Maeda4, Takashi Hirano5, Hirohito Tsubouchi2 and Hiromasa Inoue1*

Author affiliations

1 Department of Pulmonary Medicine, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima, 890-8520, Japan

2 Department of Digestive and Lifestyle Related Disease, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan

3 Department of Surgical Oncology and Digestive Surgery, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan

4 Department of Research & Development, Immuno-Biological Laboratories Co., Ltd, Fujioka, Gunma, Japan

5 Todachuo General Hospital, Toda, Saitama, Japan

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Citation and License

BMC Pulmonary Medicine 2012, 12:55  doi:10.1186/1471-2466-12-55

Published: 11 September 2012



Napsin A, an aspartic protease, is mainly expressed in alveolar type-II cells and renal proximal tubules and is a putative immunohistochemical marker for pulmonary adenocarcinomas. This study sought to determine whether napsin A could be measured in the serum to evaluate its relationship to idiopathic pulmonary fibrosis (IPF) and determine whether renal dysfunction might affect serum napsin A levels.


Serum levels of napsin A were measured in 20 patients with IPF, 34 patients with lung primary adenocarcinoma, 12 patients with kidney diseases, and 20 healthy volunteers. Surfactant protein (SP)-A, SP-D, and Krebs von den Lungen-6 (KL-6) levels in serum and pulmonary function tests were also evaluated in IPF patients.


Circulating levels of napsin A were increased in patients with IPF, as compared with healthy controls, and they correlated with the severity of disease. Moreover, the serum napsin A levels were not elevated in patients with pulmonary adenocarcinoma or renal dysfunction. The distinguishing point between IPF and the controls was that the area under the receiver operating characteristic curve (ROC) of napsin A was larger than that of KL-6, SP-A, or SP-D.


These findings suggest that serum napsin A may be a candidate biomarker for IPF.

Biomarker; Idiopathic interstitial pneumonia; KL-6; Napsin A; SP-A; SP-D