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 re covered by lavage before lobe resection from patients with a central bronch ial tumor, not involving the pleura, and from patients with pulmonary chond roma, intrapulmonary hemorrhage, and pneumothorax. Analysis of surface anti gens, phagocytosis capacity, and cytokine production was done in comparison to the regular CD14(++) blood monocytes and the recently described blood m onocyte subset CD14(+)CD16(+) monocytes. When defining fluorescence intensi ty 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 toget her, when compared to blood monocytes, PLM appear to represent a cell-type intermediate of regular CD14++ monocytes and the CD14+CD16+ subset. In func tional studies, we demonstrate that PLM can perform efficient Fc-receptor-m ediated phagocytosis of antibody-coated sheep red blood cells. Compared wit h 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 lipop olysaccharide stimulation. This first characterization of normal, noneffusi on human PLM can form the basis for a better interpretation of findings in malignant and inflammatory exsudates.