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Pulmonary lysozyme--a secretory protein of type II pneumocytes in the rat
G Singh1, S L Katyal, W E Brown
1Department of Pathology, University of Pittsburgh School of Medicine, PA.
Abstract:
A 14 kDa basic protein isolated from rat lung lavage was demonstrated to be lysozyme by its amino acid sequence analysis. An antiserum to rat lysozyme stained type II pneumocytes and alveolar macrophages. In rat lungs, no staining of the airway cells was noted. Lysozyme was detectable in type II pneumocytes by immunocytochemistry and by a quantitative immunoassay of lung homogenates of fetal lungs at Day 20 of gestation. An increase in the lysozyme content of the lung with increasing gestational and postnatal age of the rat was noted. In adult animals, lysozyme accounts for about 169.0 micrograms/g of wet lung weight and 0.3% of the soluble proteins in lung homogenate. Lysozyme constitutes about 6.6% of the total soluble proteins in rat lung lavage. Metabolic labeling and immunoprecipitation were used to demonstrate that rat type II pneumocytes synthesize and secrete lysozyme in vitro. However, in human lungs, lysozyme was identified in serous submucosal glands but not in alveolar type II pneumocytes. The results demonstrate differential distribution of a secretory protein in rodent and human lungs and indicate that in the rat lysozyme could be used as an immunohistologic marker for type II pneumocytes and as an indicator of secretory activity and maturation of type II pneumocytes.
Insights
Rat lung lavage revealed lysozyme, a protein primarily found in type II pneumocytes and alveolar macrophages. This protein
Area of Science:
- Pulmonary Biology
- Cellular Biology
- Biochemistry
Background:
- Lysozyme is an enzyme with antimicrobial properties.
- Its presence and function in lung tissue, particularly in specific cell types, require further investigation.
Purpose of the Study:
- To identify and characterize lysozyme in rat lung tissue.
- To determine the cellular localization and developmental expression of lysozyme in rat lungs.
- To compare the distribution of lysozyme in rat and human lungs.
Main Methods:
- Amino acid sequence analysis to identify the protein.
- Antiserum production and immunocytochemistry for cellular localization.
- Quantitative immunoassay for lysozyme content.
- Metabolic labeling and immunoprecipitation to assess synthesis and secretion.
- Comparison of lung tissue from fetal and adult rats, and human lung samples.
Main Results:
- A 14 kDa basic protein in rat lung lavage was identified as lysozyme.
- Lysozyme was localized to type II pneumocytes and alveolar macrophages in rat lungs, but not airway cells.
- Lysozyme was detectable in fetal rat lungs and increased with gestational and postnatal age.
- Rat type II pneumocytes synthesize and secrete lysozyme in vitro.
- In contrast, human lungs showed lysozyme in submucosal glands, not in type II pneumocytes.
Conclusions:
- Lysozyme is differentially distributed in rodent and human lungs.
- In rats, lysozyme serves as a marker for type II pneumocytes.
- Lysozyme expression indicates secretory activity and maturation of type II pneumocytes in rats.