The peripheral blood mononuclear leukocytes
(PBMLs) were isolated by appropriate density-gradient centrifugation
(500 X g for 30 mm) on Ficoll-Hypaque (Sigma, St
Louis) gradients, washed three times, and resuspended in appropriate
concentrations for the particular assay being used, in
suspension medium RPMI 1640 (Gibco Canada, Burlington,
Ontario) supplemented with 10% autologous serum.