FUNCTIONAL, MORPHOLOGICAL, AND PHENOTYPICAL DIFFERENCES BETWEEN RAT ALVEOLAR AND INTERSTITIAL MACROPHAGES

Alveolar macrophages (AM) and interstitial macrophages (IM) from rat l ungs were characterized with respect to morphology, phagocytosis, adhe sion properties, and phenotype. AM were recovered by lung lavage and I M by treatment of the lung tissue with DNAse and collagenase. The AM w ere enzyme treated in the same way as the IM. The IM were smaller than AM and had a higher nuclear to cytoplasm ratio. They had markedly low er phagocytic capacity. The attachment of particles to the cell surfac e was significantly lower in IM than in AM, but the capacity to ingest the particles was the same. Adherence to vitronectin- as well as fibr onectin-coated surfaces was significantly higher in AM. The phagolysos omal pH was similar in IM and AM, around pH 5, indicating that dissolu tion of inorganic particles can take place effectively also in IM. Fiv e surface receptors were studied, and the expression differed signific antly in all five between AM and IM. The expression of OX-1 (CD 45), a common leukocyte antigen, was significantly higher on AM as was the e xpression of CD 71 (transferrin receptor). The receptor density for OX -42 was higher on a fraction of IM. This might be compatible with a st ronger interaction between these cells and, for example, matrix compon ents. IM had more surface antigen expressing MHC class Ia (OX-6) and C D 54. Both receptors are important for the antigen presentation capaci ty of macrophages. These findings show profound differences in phenoty pe between AM and IM and indicate that IM is a highly immunocompetent cell and should not be regarded only as a precursor to AM.