Notch signaling licenses allergic airway inflammation by promoting Th2 cell lymph node egress.

Allergic asthma is mediated by Th2 responses to inhaled allergens. Although previous experiments indicated that Notch signaling activates expression of the key Th2 transcription factor Gata3, it remains controversial how Notch promotes allergic airway inflammation. Here we show that T cell-specific Notch deficiency in mice prevented house dust mite-driven eosinophilic airway inflammation and significantly reduced Th2 cytokine production, serum IgE levels, and airway hyperreactivity. However, transgenic Gata3 overexpression in Notch-deficient T cells only partially rescued this phenotype. We found that Notch signaling was not required for T cell proliferation or Th2 polarization. Instead, Notch-deficient in vitro-polarized Th2 cells showed reduced accumulation in the lungs upon in vivo transfer and allergen challenge, as Notch-deficient Th2 cells were retained in the lung-draining lymph nodes. Transcriptome analyses and sequential adoptive transfer experiments revealed that while Notch-deficient lymph node Th2 cells established competence for lung migration, they failed to upregulate sphingosine-1-phosphate receptor 1 (S1PR1) and its critical upstream transcriptional activator Krüppel-like factor 2 (KLF2). As this KLF2/S1PR1 axis represents the essential cell-intrinsic regulator of T cell lymph node egress, we conclude that the druggable Notch signaling pathway licenses the Th2 response in allergic airway inflammation via promoting lymph node egress.

A pathophysiological role of PDE3 in allergic airway inflammation.

Phosphodiesterase 3 (PDE3) and PDE4 regulate levels of cyclic AMP, which are critical in various cell types involved in allergic airway inflammation. Although PDE4 inhibition attenuates allergic airway inflammation, reported side effects preclude its application as an antiasthma drug in humans. Case reports showed that enoximone, which is a smooth muscle relaxant that inhibits PDE3, is beneficial and lifesaving in status asthmaticus and is well tolerated. However, clinical observations also showed antiinflammatory effects of PDE3 inhibition. In this study, we investigated the role of PDE3 in a house dust mite-driven (HDM-driven) allergic airway inflammation (AAI) model that is characterized by T helper 2 cell activation, eosinophilia, and reduced mucosal barrier function. Compared with wild-type (WT) littermates, mice with a targeted deletion of the PDE3A or PDE3B gene showed significantly reduced HDM-driven AAI. Therapeutic intervention in WT mice showed that all hallmarks of HDM-driven AAI were abrogated by the PDE3 inhibitors enoximone and milrinone. Importantly, we found that enoximone also reduced the upregulation of the CD11b integrin on mouse and human eosinophils in vitro, which is crucial for their recruitment during allergic inflammation. This study provides evidence for a hitherto unknown antiinflammatory role of PDE3 inhibition in allergic airway inflammation and offers a potentially novel treatment approach.

Bruton's tyrosine kinase mediated signaling enhances leukemogenesis in a mouse model for chronic lymphocytic leukemia.

In chronic lymphocytic leukemia (CLL) signals from the B cell receptor (BCR) play a major role in disease development and progression. In this light, new therapies that specifically target signaling molecules downstream of the BCR continue to be developed. While first studies on the selective small molecule inhibitor of Bruton's tyrosine kinase (Btk), Ibrutinib (PCI-32765), demonstrated that Btk inhibition sensitizes CLL cells to apoptosis and alters their migratory behavior, these studies however did not address whether Btk-mediated signaling is involved in the process of CLL leukemogenesis. To investigate the requirement of Btk signaling for CLL development, we modulated Btk expression in the IgH.ETµ CLL mouse model, which is based on sporadic expression of the simian oncovirus SV40 T-antigen in mature B cells. To this end, we crossed IgH.ETµ mice on a Btk-deficient background or introduced a human Btk transgene (CD19-hBtk). Here we show that Btk deficiency fully abrogates CLL formation in IgH.ETµ mice, and that leukemias formed in Btk haplo-insufficient mice selectively expressed the wild-type Btk allele on their active X chromosome. Conversely, Btk overexpression accelerated CLL onset, increased mortality, and was associated with selection of non-stereotypical BCRs into CLL clones. Taken together, these data show that Btk expression represents an absolute prerequisite for CLL development and that Btk mediated signaling enhances leukemogenesis in mice. We therefore conclude that in CLL Btk expression levels set the threshold for malignant transformation.