Role of Tec family kinases Itk and Btk in FceRI mediated Mast cell signaling
Open Access
- Author:
- Iyer, Archana Sriram
- Graduate Program:
- Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 01, 2008
- Committee Members:
- Avery August, Committee Chair/Co-Chair
Margherita Teresa Anna Cantorna, Committee Member
Richard John Frisque, Committee Member
Andrew Thomas Henderson, Committee Member
Robert Paulson, Committee Member
Peter John Hudson, Committee Member - Keywords:
- Mast cells
Itk
Btk
FceRI - Abstract:
- Fc epsilon Receptor I (FcεRI) signaling in Mast Cells (MCs) play an important role in IgE mediated allergic reactions such as anaphylaxis and allergic asthma. Antigen cross-linking of IgE bound to the FcεRI releases proinflammatory mediators that can cause vasodilation, mucous secretion, activation and recruitment of other inflammatory cells. Itk and Btk are critical signal amplifiers downstream of TCR and BCR, respectively. Although both are expressed in MCs, their relative importance in FcεRI signaling is not clear. Mice lacking Itk exhibit impaired Th2 cytokine secretion and reduced immunological symptoms during allergic airway responses. However, they have increased levels of circulating serum IgE. We have examined the role of Itk in MC function and FcεRI signaling. We report here that Itk null mice have reduced allergen/IgE induced histamine release as well as early airway hyperresponsiveness in vivo. This is due to the increased levels of IgE in the serum of these mice, which precludes the binding of antigen specific IgE on MCs. The transfer of Itk-/- BMMCs into MC deficient W/Wv animals is able to completely rescue histamine release in these mice. Further analysis of Itk-/- BMMC in vitro revealed that while they have normal degranulation responses, they secrete elevated levels of cytokines, including IL-13 and TNF-α. Analysis of biochemical events downstream of the FcεRI revealed little difference in overall tyrosine phosphorylation of specific substrates or calcium responses,however, these cells express elevated levels of NFAT. Microarray analysis suggests that Itk can regulate FcεRI mediated gene expression.To evaluate the potential specific and redundant functions of Itk and Btk in FcεRI mediated signaling, we generated the Itk/Btk DKO mice. These mice have reduced MC granularity and impaired responses to systemic anaphylaxis in vivo. We characterized the biochemical responses to FcεRI using Itk/BTK DKO BMMCs. In vitro analysis suggests that the downstream signaling responses in Itk/Btk DKO BMMCs are very similar to those observed in Btk-/- BMMCs. Specifically calcium responses, PLCγ2 phosphorylation and degranulation were found to be impaired. However, phosphorylation of Erk was not affected in the Itk/Btk DKO BMMCs, suggesting that Erk/MAPK activation in FcεRI signaling is independent of Itk and Btk. In addition to the impairment of MC responses, the Itk/Btk DKO mice have multiple defects in lymphoid development. They have reduced CD4+ T cells due to absence of Itk and reduced B cells due to the loss of Btk. These mice have extremely high levels of serum IgE, suggesting that both, Itk and Btk are required for mediating B cell class switch to IgE. Overall our results suggest that Tec kinases have cell type specific function. Thus while Itk plays a more critical role in T cell function, it may play a more specialized role in MCs. Our data also supports the idea that Itk and Btk have unique roles in FcεRI signaling cells and both kinases are required for optimal MC function in vivo. Btk is more important for early response such as phosphorylation of PLCγ2 and Ca2+ mobilization. While Itk plays a more specialized role by regulating the late responses such as changes in gene expression and cytokine secretion.