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

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Abstract
To analyze the NF-κB/Rel activity pattern in a living organism, we previously generated transgenic mice carrying a κB-dependent lacZ gene. In situ analysis of both primary and secondary lymphoid organs revealed a strong NF-κB 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-β-D-galactopyranoside (FDG) as a vital substrate for the β-galactosidase, we re-examined by flow cytometry the NF-κB/Rel transcriptional activity in our mouse model. We report here that such constitutive NF-κB/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-κB/Rel activity was found in most B cells, unlike T cells which were largely negative. Virgin IgD+ B cells expressed higher levels of NF-κB transcriptional activity than other B cell types. Altogether, these results suggest that NF-κB/Rel complexes are key players in the in vivo differentiation of IgD+ B lymphocytes and possibly CD25+ thymocytes.