Immunologic characterization of normal human pleural macrophages

Human pleural macrophages (PLM) have been studied in effusions, but little is known about normal human PLM. We therefore analyzed resting human PLM recovered by lavage before lobe resection from patients with a central bronchial tumor, not involving the pleura, and from patients with pulmonary chondroma, intrapulmonary hemorrhage, and pneumothorax. Analysis of surface antigens, phagocytosis capacity, and cytokine production was done in comparison to the regular CD14(++) blood monocytes and the recently described blood monocyte subset CD14(+)CD16(+) monocytes. When defining fluorescence intensity for the various markers on CD14(++) monocytes as 100%, the PLM gave the following pattern: CD14, 45%; CD32, 200%; CD64, 72%; CD11b, 128%; CD33, 74%; CD54, 299%; and HLA-DR, 1,906%. When CD16 on the CD14(+)CD16(+) monocytes was set as 100%, the level of CD16 expression on PLM was 7.7%. Taken together, when compared to blood monocytes, PLM appear to represent a cell-type intermediate of regular CD14++ monocytes and the CD14+CD16+ subset. In functional studies, we demonstrate that PLM can perform efficient Fc-receptor-mediated phagocytosis of antibody-coated sheep red blood cells. Compared with blood monocytes, the capacity of PLM to produce tumor necrosis factor is similar, but a striking finding in PLM was the constitutive interleukin-10 messenger RNA expression that could not be substantially increased by lipopolysaccharide stimulation. This first characterization of normal, noneffusion human PLM can form the basis for a better interpretation of findings in malignant and inflammatory exsudates.