text: Isolation of CD4+ T cells
  Peripheral blood mononuclear cells (PBMC) were prepared from heparinized blood samples by centrifugation over Ficoll-Hypaque density gradients (Pharmacia, Uppsala, Sweden). CD4+ T cells were purified from PBMC by positive selection using anti-CD4 mAb-coated magnetic beads (Miltenyi Biotec, Gladbach, Germany), according to the manufacturer's instructions. CD4+ T cells were isolated from ST samples, as previously described [27]. Briefly, fresh ST samples were fragmented and digested with collagenase and DNase for 1 hour at 37degreesC. After removing tissue debris, ST cell suspensions in culture medium (RPMI 1640 medium; Life Technologies, Gaithersburg, MD, USA) supplemented with 25 mM HEPES (2 mM L-glutamine, 2% nonessential amino acids, 100 IU/ml penicillin, and 100 mg/ml streptomycin; Life Technologies) with 10% heat-inactivated FCS (Life Technologies) were incubated at 37degreesC in six-well plates (Coster, Cambridge, MA, USA) for 45 min. Non-adherent cells were harvested and CD4+ T cells were purified by positive selection as already described. 
  