CO2 euthanasia, LN were resected and either fixed in 4% neutral-buffered formalin or minced in phosphatebuffered saline (PBS) and filtered through a 35-μm nylon mesh; 7-μm paraffin-embedded, formalin-fixed LN sections were stained with hematoxylin-eosin (HE) to evaluate apoptotic cell morphology. Single cell suspensions were plated on irradiated (30 Gy) feeder layer (2.5 x 105 NIH-3T3 cells/10-cm plate) in 45% Iscove’s modified Eagle medium, 45% Dulbecco’s minimal essential medium, 10% fetal bovine serum, 100 units/ml penicillin and streptomycin, 4 mM L-glutamine, and 25 μM 2-mercaptoethanol. Genomic DNA was isolated by proteinase K digest after short-term culturing to eliminate contaminating normal cells.