Figure 3: ARPC1B-null and Wiskott–Aldrich syndrome platelets are similar.

(a) Transmission electron microscopy (TEM) imaging of sections from normal donor, ARPC1B-null (Patient 1) and WASP-null patient platelets show typical structures including α-granules (white arrows), mitochondria (black arrows) and internal membrane systems (bars=500 nm; see Fig. 4 for further comparisons). (b) Immunofluorescence microscopy of cells stained for circumferential ring tubulin (green) and α-granule membrane P-selectin (red) shows that ARPC1B-null and WASP-null platelets appear small and dysmorphic compared to normal (bars=5 μm). (c) A comparison of circumferential ring diameter distributions confirmed that both ARPC1B-null and WASP-null platelets are significantly smaller than normal (P<0.0001, unpaired t-test; n=57 cells; 95% confidence intervals shown) and do not differ significantly from each other. Equivalent comparisons of all patients with WASP-null and normal control platelets is shown in Fig. 5a. (d) The morphology of a normal platelet showing the typical subcellular locations of tubulin (magenta), P-selectin (red) and α-granule cargo thrombospondin-1 (TSP1, green; bars=1 μm). (e) Collections of representative cells illustrate the range of abnormal features observed in ARPC1B-null and WASP-null platelets, including small size and the variable absence of internal contents (bars=1 μm).