Peripheral blood phenotyping. (A) Flow cytometric detection of CD18 expression of peripheral blood neutrophils and lymphocytes in 3 LAD-1 patients and a healthy control. CD18 expression is shown as histograms. For PMNs, anti-CD18 antibody binding is expressed as relative fluorescence intensity (RFI), defined as geometric mean channel (GMC) fluorescence of CD18 FITC divided by GMC fluorescence of isotype control. For lymphocytes, percentage of lymphocytes staining positive for CD18 is shown. All 3 patients have a lymphocyte population distinctly positive for CD18 compared with the rest of the lymphocyes. The solid peaks represent CD18, while dashed lines represent the isotype controls. (B) Four-color flow cytometry analysis of PBMCs from 3 patients with LAD-1. Backgating and multigating techniques were used to assess coexpression of multiple cell surface markers on CD18⁺ lymphocytes. CD18 is expressed on the x-axis of all dot plots, while the indicated surface antibody is shown on the y-axis. CD18 was coexpressed with CD3 and CD8 but not with CD4 or CD20. CD18⁺ T cells did not stain with CD27 or CD28 (data not shown). TCR staining revealed more than 95% TCRαβ⁺ in the CD3⁺/CD18⁺ population. Patients 1 and 2 had small populations of CD18⁺ cells carrying NK (CD3⁻/CD56⁺/16⁺) cell surface markers (1% and 5% of all CD18⁺ cells, respectively).