LOCALIZATION OF SURFACTANT PROTEIN-A (SP-A) IN ALVEOLAR MACROPHAGE SUBPOPULATIONS OF NORMAL AND FIBROTIC RAT LUNG

The colocalization of surfactant protein A (SP-A) and the alveolar mac rophage markers ED1 and RM-1, as well as various lectins of the N-acet yl-galactosamine group [Maclura pomifera lectin (MPA), Dolichos biflor us lectin (DBA), soybean agglutinin (SBA)] and of the mannose group [C anavalia ensiformis lectin (ConA), Galanthus nivalis lectin (GNA)] was studied in normal and fibrotic rat lung tissues. In normal tissue, SP A was located preferentially in the alveolar macrophage subpopulation lacking specific binding sites for lectins of the N-acetylgalactosami ne group (DBA and SBA), although 50% of MPA-binding macrophages contai ned SP-A. The ED1-positive cells were SP-A-negative, whereas SP-A upta ke could be detected among the RM-1 immunoreactive as well as the ConA and GNA binding macrophages. In fibrotic lung tissue, however, a smal l number of DBA and SBA binding macrophages contained SP-A and the per centage of GNA and ConA binding alveolar macrophages exhibiting SP-A i mmunoreactivity was reduced. Additionally, the number of ED1(+)/SP-A() macrophages was found to be increased. Immunoelectron microscopy rev ealed accumulation of SP-A in the extracellular space. The differing S P-A content in different alveolar macrophage subpopulations suggests a more complex mechanism of uptake and degradation of surfactant protei ns in normal and pathological conditions, which cannot simply be expla ined by the glycoconjugate pattern on the surface of alveolar macropha ges.