Expression of the RelB transcription factor correlates with the activationof human dendritic cells

The RelB gene product is a member of the nuclear factor (NF)-kappa B family of transcription factors. It has been identified recently within mouse ant igen-presenting cells and human monocyte-derived dendritic cells (DC). Disr uption of the mouse RelB gene is accompanied, amongst other phenotypes, by abnormalities in the antigen-presenting cell lineages. In order to define R elB expression during human DC differentiation, we have analysed RelB mRNA by reverse transcriptase-polymerase chain reaction and RelB protein by intr acellular staining in CD34(+) precursors and different types of DC preparat ions. RelB mRNA was not detected in CD34+ precursor populations. Fresh bloo d DC (lineage-human leucocyte antigen-DR+ (lin (-)HLA-DR+)) lacked RelB mRN A and cytoplasmic RelB protein but a period of in vitro culture induced Rel B expression in blood DC. Purified Langerhans' cells (LC) (CD1a(+) HLA-DR+) failed to express RelB mRNA. Immunocytochemical staining identified RelB p rotein in human skin epithelium. RelB protein was expressed in a very few C D1a(+), CD83(+) or CMRF-44(+) dermal DC but was not present in CD1a(+) LC. Tonsil DC (lin (-)HLA-DR+ CMRF-44+) were positive for RelB mRNA and RelB pr otein. Intestinal DC (HLA-DR+) also lacked immunoreactive RelB protein. The majority of interdigitating CD83+, CMRF-44(+), CMRF-56(+) or p55(+) DC loc ated in paracortical T-lymphocyte areas of lymph node and tonsil contained RelB protein. The expression of RelB mRNA and RelB protein correlates with the activated phase of blood DC and the postmigration cell (activated) stag e of tissue DC development.