Surfactant protein D expression in normal and pneumonic ovine lung.
Surfactant protein D (SP-D) is a collagenous calcium-dependent lectin constitutively expressed by alveolar type II pneumocytes and non-ciliated bronchiolar epithelial (Clara) cells. It binds to surface glycoconjugates expressed by a wide variety of microorganisms such as Gram-negative bacteria, influenza A virus, and various fungi, leading to pathogen inactivation or enhanced neutrophil and macrophage activity. Since a hallmark of bronchopneumonia is the initiation of inflammation in the bronchi and bronchoalveolar junction, we chose a classic ruminant model of bronchopneumonia caused by Mannheimia haemolytica to study the expression of SP-D within the bronchioles of infected lambs. Healthy weaned lambs were inoculated with either pyrogen-free saline (controls) or M. haemolytica intrabronchially using a fiber-optic bronchoscope. SP-D protein and mRNA expression in lung was detected by immunohistochemistry (IHC) and fluorogenic real-time relative quantitative reverse transcriptase polymerase chain reaction (real-time RT-PCR), respectively, during acute (1 day), subacute (15 days), and chronic (45 days) bronchopneumonia. At 15 and 45 days post-inoculation, areas of lung had peribronchiolar inflammatory cell infiltrate, epithelial cell hyperplasia, tortuosity of the airway lumens, and decreased intensity of SP-D protein staining and number of positive cells. The levels of SP-D mRNA were not increased or significantly altered by M. haemolytica infection when compared to control animals. In conclusion, cell-associated SP-D protein expression significantly decreases within hyperplastic epithelium of lungs from infected animals during chronic bronchopneumonia. Exhaustion of SP-D protein reserves and absence of SP-D gene upregulation during the progression of bacterial pneumonia into chronicity may result in failure to clear the pathogen from the lung and/or cause animals to be more susceptible to re-infection.
Grubor
Branka
B
Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Veterinary Medicine, Ames, IA 50011-1250, USA. brankag@iastate.edu
Gallup
Jack M
JM
Ramírez-Romero
Rafael
R
Bailey
Ted B
TB
Crouch
Erika C
EC
Brogden
Kim A
KA
Ackermann
Mark R
MR
D000818:Animals; D004847:Epithelial Cells / Q000276:immunology / Q000378:metabolism; D005260:Female; D007150:Immunohistochemistry / Q000662:veterinary; D008297:Male; D016978:Mannheimia haemolytica / Q000276:immunology*; D012766:Pasteurellosis, Pneumonic / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology; D037663:Pulmonary Surfactant-Associated Protein D / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011897:Random Allocation; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology
D037663:Pulmonary Surfactant-Associated Protein D; D012333:RNA, Messenger