Dendritic cells (DC) are professional antigen-presenting cells that are able to induce primary T cell responses. Therefore, several strategies employ peptide-pulsed DC in tumor immunotherapy. For efficient antigen presentation and induction of an immune response by DC the number and stability of MHC I-peptide complexes is crucial. We studied this issue by using the antibody 25-D1.16 that specifically detects OVA peptide SIINFEKL in conjunction with H-2 Kb molecules, and determined its kinetics on mature and immature bone marrow-derived murine DC. Optimal peptide loading was reached after 8-16 h at 50 microM peptide pulse, and was comparable in serum-free versus serum-containing medium. Stimulation of DC with LPS or Poly I:C, and to a lesser extent TNF-alpha, upregulated the total number of surface MHC I molecules and thus improved peptide loading. Pulse-chase experiments revealed a constant half-life of peptide/Kb complexes independent of preceding DC stimulation or their maturation stage. The duration of peptide/Kb complex expression on mature DC, however, could be extended from 24 h to 72 h when the cultures were pretreated with LPS or Poly I:C, but not TNF-alpha. These data might have important implications for the clinical application of peptide-pulsed DC in tumor immunotherapy.