Defective cell death induction by Fas triggering in T cells from patients with ALD and not in patients with typical chronic ITP. Fas was triggered with anti-Fas MoAb (lanes a and b) or anti-Fas MoAb + anti-IgM serum (lanes c and d), and cell survival was assessed after 18 (lanes a and c) or 48 hours (lanes b and d) by the trypan blue exclusion test. Results are expressed as percentage of specific cell survival (see the Materials and Methods). Statistical analysis is reported in Table 2.