Phenotypical characterization of ARPC1B-deficient patients. (A) Histograms showing ARPC1B expression in T, B, NK cells, and monocytes in patients included in the study (blue lines) and their healthy controls (HC; blue tinted lines) determined by flow cytometry. Red filled lines: negative controls of patients. Red dashed lines: negative controls of HC. Percentage of ARPC1B⁺ in patients’ cells is indicated. (B) Confocal microscopy of ARPC1B, F-actin, merged with nuclei (DAPI) in a representative field of HC, P1, P2, and P7 (ARPC1B-null patient) peripheral blood lymphocytes. Bar represents 10 μm. Arrows indicate positive staining for ARPC1B and F-actin.