ABSTRACT
Delipidated proteins from a fraction of mouse lung homogenate enriched for lamellar bodies of type 2 pneumocytes were characterized by a combination of gel filtration and enzyme immunoassay for the presence of a surfactant-associated antigen. Immunoreactivity was associated with a protein of Mr 250-270,000 as well as its multimers and proteolytic fragments. The characteristics of the antigenic protein closely resembled those of a surfactant-associated protein termed alveolyn which is reported to be secreted by type 2 pneumocytes of various other species. Surfactant-associated proteins of M 32-38,000 in bronchoalveolar lavage fluid may be derived from this molecule by proteolysis.
Subject(s)
Glycoproteins/analysis , Lung/cytology , Animals , Chromatography, Gel , Immunoenzyme Techniques , Lung/analysis , Mice , Molecular Weight , Peptide Fragments/analysis , Pulmonary Alveoli/analysis , Pulmonary Surfactant-Associated Protein A , Therapeutic IrrigationABSTRACT
Hypertrophy and hyperplasia of type 2 pneumocytes during the evolution of subacute and chronic pulmonary injury cannot always be satisfactorily explained in terms of reparative responses to type 1 pneumocyte injury. We hypothesized that immunocompetent cells, evoked as part of the interstitial inflammatory response, may be secreting factors which affect proliferation and surfactant biosynthesis by type 2 pneumocytes. To evaluate this hypothesis in vitro, we tested the effects of lymphokine-enriched supernatants, from serum-free cultures of concanavalin A-stimulated spleen cells, upon the type 2 pneumocyte-related cell strain NAL 1A. Addition of these supernatants in culture induced irreversible morphologic and ultrastructural alterations in the NAL 1A cells, inhibited cell replication, and evoked increased and apparently abnormal surfactant phospholipid biosynthesis. Supernatants from unstimulated spleen cells had no effect. There was no evidence of toxic injury to the cells in culture, and an immunologically specific cytoplasmic protein continued to be expressed. The active factor(s) appeared to be a protein or peptide of greater than 10,000 molecular weight. A specific soluble factor such as is present in the mitogen-stimulated lymphoid cell supernatants may be capable of mediating a similar interaction with type 2 pneumocytes in vivo.
Subject(s)
Lymphokines/pharmacology , Pulmonary Alveoli/cytology , Animals , Cell Division , Cell Line , Concanavalin A/pharmacology , Female , Lymphocyte Activation , Mice , Phospholipids/metabolism , Proteins/metabolism , Pulmonary Alveoli/injuries , Pulmonary Alveoli/metabolism , Spleen/immunologyABSTRACT
The mouse lung epithelial cell strain NAL 1A has been confirmed as type 2 pneumocyte-related by immunostaining with a type 2 pneumocyte-specific antiserum. Cytoplasmic immunoreactivity with the antiserum paralleled the appearance of phospholipid-containing osmiophilic cytoplasmic inclusions, which were much more abundant in confluent cell cultures at low passage number than in exponentially growing cultures. However, phospholipid analysis indicated that NAL 1A cells were impoverished in phosphatidylglycerol as compared to lung type 2 pneumocytes. Confluent cultures of the neoplastic cell lines NAL 1AM and NUL 1 did not reveal any reactivity with the specific antiserum.
