c-Rel is a member of the Rel/NF-kappaB transcription factor family that forms homo or heterodimers with family members such as RelA/p65, RelB, NF-kappaB1/p105, and NF-kappaB2/p100. The NF-kappaB complex is retained in cytoplasm by the inhibitor IkappaB protein in unstimulated cells. Upon activation, IkappaB is degraded via the ubiquitin-proteasome pathway, which results in nuclear translocation of the active NF-kappaB complex. While other NF-kappaB transcription factors are expressed in most cell types, relatively higher levels of c-REL expression are found in hematopoietic cells. c-REL is thought to play key roles in regulating proliferation, differentiation, and survival of B and T lymphocytes.