Calprotectin expression and mononuclear phagocyte subpopulations in peripheral blood and bronchoalveolar lavage

Background and aim of the work. The phenotype of human alveolar macrophages (AM) can be affected by the process of maturation/differentiation and by m ultiple factors from the local environment. The aim of our study was to ass ess the expression of selected phenotypic markers characteristic for subset s of mononuclear phagocytes in bronchoalveolar lavage fluid (BAL) and perip heral blood with special attention to calprotectin (27E10), a marker of acu te inflammatory macrophages. Methods. The expression of calprotectin and 13 other phenotypic markers was evaluated by an immunoperoxidase slide assay and computer image analysis. Results. We consider calprotectin (27E10 antig en) to be a marker of freshly recruited, monocyte-like, mononuclear phagocy tes. being expressed in 84 +/- 13% PBM and only 10 +/- 11% Cre of AM, p < 0 .001. Computer image analysis confirmed that calprotectin-positive mononucl ear cells in peripheral blood and BAL are morphologically very similar in c ontrast to the much larger calprotectin-negative AM. On the other hand, 25F 9 antigen, the transferrin receptor (CD71), KiM8 (CD68), RFD1 (marker of de ndritic cells), RFD7 (marker of mature macrophages), RFD9 (marker of epithe lioid cells and macrophages of germinal centers), and RM3/1 (macrophages of late phase inflammation) were restricted preferentially to mature AM. Conc lusions. Our study demonstrates phenotypic differences between mononuclear phagocytes derived from BAL and their peripheral blood precursors, and indi cates markers useful for assessing the stages of maturation/differentiation of these cells. The percentage of calprotectin (27E10) positive AM might r epresent a parameter for assessing mononuclear phagocyte influx from periph eral blood to the lung in the very early stage of inflammatory reactions.