Surfactant protein D expression in normal and pneumonic ovine lung.

Abstract

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.

• Authors: Branka Grubor, Jack M Gallup, Rafael Ramírez-Romero, Ted B Bailey, Erika C Crouch, Kim A Brogden, Mark R Ackermann
• Journal: Veterinary immunology and immunopathology (Vet Immunol Immunopathol) Vol. 101 Issue 3-4 Pg. 235-42 (Oct 2004) ISSN: 0165-2427 [Print] Netherlands
• PMID: 15350753 (Publication Type: Journal Article, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Pulmonary Surfactant-Associated Protein D
• RNA, Messenger

Topics

• Animals
• Epithelial Cells (immunology, metabolism)
• Female
• Immunohistochemistry (veterinary)
• Male
• Mannheimia haemolytica (immunology)
• Pasteurellosis, Pneumonic (immunology, metabolism, microbiology, pathology)
• Pulmonary Surfactant-Associated Protein D (biosynthesis, genetics, immunology)
• RNA, Messenger (biosynthesis, genetics)
• Random Allocation
• Reverse Transcriptase Polymerase Chain Reaction (veterinary)
• Sheep
• Sheep Diseases (immunology, metabolism, microbiology, pathology)