Ed from healthy volunteer donors. Peripheral blood mononuclear cells isolated by Ficoll-Hypaque (Pharmacia Corporation, http://www.pfizer.com) density gradient centrifugation were seeded at 6 3 106/2 ml in 12-well plates in RPMI 1640 medium and supplemented with 10 heat-inactivated human AB serum (Nabi Biopharmaceuticals, http://www.nabi.com), 50 U/ml penicillin, 50 lg /ml streptomycin, and 2 mM