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. 2004 Apr;30(4):449-58.
doi: 10.1165/rcmb.2003-0262OC. Epub 2003 Sep 11.

Surfactant protein B in type II pneumocytes and intra-alveolar surfactant forms of human lungs

Frank Brasch  1 , Georg Johnen, Alexandra Winn-Brasch, Susan H Guttentag, Andreas Schmiedl, Nadine Kapp, Yasuhiro Suzuki, Klaus M Müller, Joachim Richter, Samuel Hawgood, Matthias Ochs
Affiliations

Surfactant protein B in type II pneumocytes and intra-alveolar surfactant forms of human lungs

Frank Brasch et al. Am J Respir Cell Mol Biol. 2004 Apr.

Abstract

Surfactant protein B (SP-B) is synthesized by type II pneumocytes as a proprotein (proSP-B) that is proteolytically processed to an 8-kD protein. In human type II pneumocytes, we identified not only proSP-B, processing intermediates of proSP-B, and mature SP-B, but also fragments of the N-terminal propeptide. By means of immunoelectron microscopy, proSP-B and processing intermediates were localized in the endoplasmic reticulum, Golgi vesicles, and few multivesicular bodies in type II pneumocytes in human lungs. A colocalization of fragments of the N-terminal propeptide and mature SP-B was found in multivesicular, composite, and some lamellar bodies. Mature SP-B was localized over the projection core of lamellar bodies and core-like structures in tubular myelin figures. In line with immunoelectron microscopy and Western blot analysis of human type II pneumocytes, a fragment of the N-terminal propeptide was also detected in isolated rat lamellar bodies. In conclusion, our data indicate that the processing of proSP-B occurs between the Golgi complex and multivesicular bodies and provide evidence that a fragment of the N-terminal propeptide and mature SP-B are transported together to the lamellar bodies. In human lungs, mature SP-B is involved in the structural organization of lamellar bodies and tubular myelin by the formation of core particles.

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