In vivo identification of lymphocyte subsets exhibiting transcriptionally active NF-κB/Rel complexes

To analyze the NF-kappa B/Rel activity pattern in a living organism, we previously generated transgenic mice carrying a kappa B-dependent lacZ gene, In situ analysis of both primary and secondary lymphoid organs revealed a strong NF-kappa B transcriptional activity in antigen-presenting cells, some endothelial cells and sinus lining cells of the lymph node capsula with very little activity in lymphocytes and thymocytes, Using fluorescein-di-beta-D-galactopyranoside (FDG) as a vital substrate for the P-galactosidase, we re-examined by flow cytometry the NF-kappa B/Rel transcriptional activity in our mouse model. We report here that such constitutive NF-kappa B/Rel activity was significantly detected in thymocytes at the CD44(+)CD25(-) stage. This constitutive activity extended with CD25 expression to the majority of the CD44(-)CD25(+) thymocytes and was then restricted to a few mature T cells. In the spleen, constitutive NF-kappa B/Rel activity was found in most B cells, unlike T cells which were largely negative. Virgin IgD(+) B cells expressed higher levels of NF-kappa B transcriptional activity than other a cell types. Altogether, these results suggest that NF-kappa B/Rel complexes are key players in the in vivo differentiation of IgD(+) a lymphocytes and possibly CD25(+) thymocytes.