Applicability of laser scanning cytometry to study paediatric alveolar macrophages

Laser scanning cytometry (LSC) generates quantitative information on immune receptor expression from cells cytocentrifuged onto a microscope slide. In children, the description of developmental changes in immune receptor expression on alveolar macrophages (AM) has been limited by the small number of cells recovered by bronchoalveolar lavage (BAL). The applicability of LSC to the study of AM from normal children was therefore assessed. AM were obtained by BAL of normal children following intubation prior to elective surgery. The ability of LSC to identify the cytoplasm of AM was assessed using either: 1) autofluorescence; 2) forward scatter; 3) nuclear staining with propidium iodide; or 4) a fluorescent-labelled monoclonal antibody to CD68, a pan-macrophage antigen. LSC could only reliably identify individual AM when stained with CD68. The sensitivity for detecting single whole AM using CD68 was 0.97 and the positive predictive value was 0.88, respectively, with excellent repeatability. In addition, a range of immunofluorescence parameters were generated for CD68. It is concluded that laser scanning cytometry is suited to the study of immune receptor expression from small numbers of paediatric alveolar macrophages, when CD68 is used for cell identification.