Immunohistochemical characteristics of surfactant proteins a, B, C and d in inflammatory and tumorigenic lung lesions of f344 rats

Abstract

Surfactant proteins (SPs), originally known as human lung surfactants, are essential to respiratory structure and function. There are 4 subtypes, SP-A, SP-B, SP-C and SP-D, with SP-A and SP-D having immunological functions, and SP-B and SP-C having physicochemical properties that reduce the surface tension at biological interfaces. In this experiment, the expressions of SP-A, SP-B, SP-C and SP-D in lung neoplastic lesions induced by N-bis (2-hydroxypropyl) nitrosamine (DHPN) and inflammatory lesions due to quartz instillation were examined and compared immunohistochemically. Formalin fixed paraffin embedded (FFPE) lung samples featuring inflammation were obtained with a rat quartz instillation model, and neoplastic lesions, hyperplasias and adenomas, were obtained with the rat DHPN-induced lung carcinogenesis model. In the rat quartz instillation model, male 10-week old F344 rats were exposed by intratracheal instillation (IT) to quartz at a dose of 2 mg/rat suspended in saline (0.2 ml) on day 0, and sacrificed on day 28. Lung tumorigenesis in F344 male rats was initiated by DHPN in drinking water for 2 weeks, and the animals were then sacrificed in week 30. Lung proliferative lesions, hyperplasias and adenomas, were observed with DHPN, and inflammation was observed with quartz. The expressions of SP-A, SP-B, SP-C and SP-D were examined immunohistochemically. SP-B and SP-C showed strong expression in lung hyperplasias and adenomas, while SP-A and SP-D were observed in mucus or exudates in inflammatory alveoli. These results suggest the possibility that SP-B and SP-C are related to lung tumorigenesis.

Keywords: DHPN; lung; quartz; rat; tumor; urfactant protein.

Fig. 1.

Histopathological and immunohistochemical findings for inflammatory lesions induced by quartz in the F344 rat lung (×200). A and D, H.E.; B and E, SP-A; C and F, SP-B; G and I, SP-C; H and J, SP-D. A, B, C, G and H, inflammatory lesions; D, E, F, I and J, noninflammatory lesions (control). Note the strong positive reactions in the mucus in the alveoli in Fig. 1-B, strongly positive staining of alveolar epithelial cells and bronchial epithelial cells in Fig. 1-C, alveolar epithelial cells in Fig. 1-G and mucus in the alveoli in Fig. 1-H.

Fig. 2.

Immunohistochemical findings for bronchiolar epithelial cells in the F344 rat lung after quartz exposure (×200). A, weak positivity (+) for SP-A; B, strong positivity (++) for SP-B; C, weak positivity (+) for SP-C; D, negative for SP-D.

Fig. 3.

Histopathological and immunohistochemical findings for DHPN-induced proliferative lesions, hyperplasias and adenomas, in the F344 rat lung (×200). A and D, H.E.; B and E, SP-A; C and F, SP-B; G and I, SP-C; H and J, SP-D. A, B, C, G and H, proliferative lesions; D, E, F, I and J, nonproliferative lesions (control). Note the weak positivity (+) for SP-A in Fig. 1-B, strong positivity (++) for SP-B in Fig. 1-C, strong positivity (++) for SP-D in Fig. 1-G and almost negative (−) staining for SP-D in Fig. 1-H.