Morphologic analysis of fresh human EBV⁺ B-cell tumors from hu-PBL-SCID mice (A and B) and from a patient with AIDS-PCNSL (C and D) in the presence of 10 μg/mL of immobilized anti-Fas M3 MoAb for 2 hours with or without a fivefold excess of soluble M3 MoAb. Morphologic characteristics of apoptosis (ie, nuclear fragmentation and membrane blebbing) are noted in (B) and (D). Wright Giemsa stain, original magnification × 330.