Identification of renin in resident alveolar macrophages and monocytes: HPLC and immunohistochemical study

Normal, unstimulated alveolar macrophages (AM) and monocytes (Mo) from both mice and rats have been shown to exhibit an angiotensin-I-forming enzyme. This protease has a similar or identical molecular weight to plasma renin as judged by HPLC analysis. In addition, the enzyme activity could be almost completely inhibited by a specific antibody to pure mouse submaxillary gland renin. This indicates that the angiotensin-I-generating protease in AM and Mo is identical to true renin. These results are in accordance with those of immunocytochemical studies, since the cells sharing immunoreactive renin are macrophages and monocytes. The low percentage of renin positive cells may indicate a functionally different and probably distinct subpopulation of AM and Mo. The presence of renin and angiotensins and angiotensin-I-converting enzyme in normal macrophages and monocytes seems to be common. Hence, the data presented raise the possibility that an intracellular renin-angiotensin system may infact exist in a certain subpopulation(s) of normal macrophages and monocytes.