Ongoing Dll4-Notch signaling is required for T-cell homeostasis in the adult thymus.

The essential role of the Delta-like ligand 4 (Dll4)-Notch signaling pathway in T-lymphocyte development is well established. It has been shown that specific inactivation of Dll4 on thymic stromal cells during early post-natal development leads to a deregulation in T-cell differentiation. However, whether ongoing Dll4-Notch signaling is required for T-cell development in the adult thymus is unknown. The use of anti-Dll4 Abs allowed us to confirm and expand previous studies by examining the kinetics and the reversibility of Dll4-Notch signaling blockade in T-cell development in adult mice. We found that anti-Dll4 treatment reduced thymic cellularity after 7 days, as a consequence of a developmental delay in T-cell maturation at the pro-T-cell double negative 1 (CD4(-) CD8(-) c-kit(+) CD44(+) CD25(-) ) stage, leading to decreased numbers of immature double-positive (CD4(+) CD8(+) ) T cells without affecting the frequency of mature single positive CD4(+) and CD8(+) thymocytes, while promoting alternative thymic B-cell expansion. This cellular phenotype was similarly observed in both young adult and aged mice (>1.5 years), extending our understanding of the ongoing role for Dll4-Notch signaling during T-cell development in the adult thymus. Finally, after cessation of Dll4 Ab treatment, thymic cellularity and thymocyte subset ratios returned to normal levels, indicating reversibility of this phenotype in both adult and aged mice, which has important implications for potential clinical use of Dll4-Notch inhibitors.

Eicosanoid-induced store-operated calcium entry in dendritic cells.

BACKGROUND: Eicosanoids are generally recognized to exert potent immunomodulatory properties, including effects on T cell, antigen-presenting cell (APC), and dendritic cell (DC) maturation and function. Since DC maturation and function may also be regulated by store-operated calcium entry (SOCE), we hypothesized that the effects of eicosanoids on DC function may in part be regulated through changes in intracellular calcium. METHODS: DC derived from the bone marrow of male Balb/ByJ mice cultured for 7 d in the presence of granulocyte macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) were used to study the effects of eicosanoids on SOCE and the resulting Ca(2+) mobilization. RESULTS: The 5-lipoxygenase (5-LO) products leukotriene B(4) (LTB(4)) and LTD(4,) but not LTC(4), depleted Ca(2+) from DC endoplasmic reticulum stores. The specificity of LTB(4) and LTD(4) on Ca(2+) store-depletion was confirmed by the ability of the specific receptor antagonists, LY25583 and MK571, respectively, to abrogate Ca(2+) store depletion. RT-PCR demonstrated DC receptors for LTB(4) (BLT(1) and BLT(2)) and the cysteinyl-LTs (CysLT(1), CysLT(2), and GPR17). We also detected transient receptor potential canonical (TRPC) 1, 2, 4, and 6 and stromal interaction molecule 1 (STIM1) on CD11c(+) DCs, suggesting these proteins also participate in DC SOCE. In contrast, the cyclooxygenase (CO) metabolite PGE(2) had no effect on DC Ca(2+) mobilization. CONCLUSIONS: To our knowledge, these are the first observations of distinct effects of eicosanoids on DC Ca(2+) mobilization, which may have important implications for the regulation of DC maturation at sites of immune and non-immune inflammation.