CD4 T cell priming in dendritic cell-deficient mice.

Bone marrow (BM) chimeras (BMC) generated from mice carrying a null (-/-) mutation in the relB gene of the NF-kappaB family represent an ideal model for in vivo studies on the role of dendritic cells (DC) in the adaptive immune response. The spleen and lymph nodes (LN) of relB(-/-) BMC contain a small number of residual DC, mainly CD8alpha(+), that fail to up-regulate MHC class II and co-stimulatory molecules after stimulation in vitro. Moreover, residual spleen DC of relB(-/-) BMC have a 4-fold decrease in the ability to uptake and process soluble model antigen, ovalbumin (OVA), and failed to prime CD4 and CD8 T cells in vitro and in vivo. In addition, they also failed to present OVA peptide to OT-II transgenic T lymphocytes at a normal 1:10 (stimulator:responder) cell ratio. In spite of these multiple DC defects, relB(-/-) BMC immunized with plasmid DNA targeted to the spleen as the site of immune induction develop a specific CD4(+) T cell response comparable to that of relB competent mice. These data demonstrate that CD4( +) T cells can be primed in the absence of functional DC and suggest that relB may gauge the T cell response in vivo.