Figure 6.

Endoplasmic reticulum (ER) stress in lung epithelial cells from infected old C57BL/6 mice. (A) Immunohistochemistry analyses of X-box–binding protein (XBP) 1 expression in lung sections of young and old mice at Day 15 of mock or MHV68 infection. Notice abundant positive staining in old MHV68-infected mice. (B) Determination of mRNA levels of unspliced and spliced XBP1 in lung samples of naive and MHV68-infected mice at Days 7 and 15 after infection. Ratio of spliced versus total XBP1 mRNA of samples is shown on the right. (C) Quantitative RT-PCR analysis for binding immunoglobulin protein (BiP) transcripts in the lungs of naive and infected young and old mice at different time point after infection (n = 3–4; *P < 0.001). (D) Immunoblot assay of lung lysates from naive (N) and infected young and old C57BL/6 mice at the indicated time point after infection using anti-BiP antibody. Blot was stripped and reprobed with an anti–β-actin antibody as a loading control. (E) Dual immunofluorescent staining in lung sections of aging mice infected at 15 dpi for pro–SP-C (green) and the markers of ER stress BiP (red) and XBP1 (red). Yellow cells in the merge column indicate type II cells supporting ER stress. Nuclei were visualized by 4′,6-diamidino-2-phenylindole staining (blue). SP-C, surfactant protein-C.