QUANTITATIVE-ANALYSIS OF LYMPHOCYTE CD11A USING STANDARDIZED FLOW-CYTOMETRY

CD11a is the alpha-subunit of the leucocyte adhesion and costimulation molecule LFA-1. We have refined the measurement of lymphocyte CD11 a density with a FACScan using commercially available fluorescent beads for standardization and fluorescein-conjugated antibody to CD11a of known fluorescein: protein ratio. The fluorescence intensity of CD11a on peripheral blood CD4+ and CD8+ lymphocytes was measured in 60 healthy subjects. We demonstrated linear correlation between age and mean CD11a density (r = 0.47 for CD4+ cells, r = 0. 71 for CD8+ cells). We established that there is a consistent logical cut off point at 4.3 x 10(3) bound antibody molecules between low-expressing and high-expressing subsets of CD8+ cells and we then investigated whether the variation in lymphocyte CD11 a expression in healthy subjects was sufficiently small for the application of this method to the detection of abnormal groups or individuals. Analysis of the CD11 a high subsets has high statistical power ( >99% in 60 subjects to detect a 25% difference) and good precision (<4% differences). The advantages of the method for comparative studies of cell surface accessory molecules are discussed. We have also evaluated a frozen cell line for quality control, and demonstrated up-regulation of CD11 a density on CD4+ and CD8+ cells measured in three patients with infectious mononucleosis.