B Cells Are Not Involved in the Regulation of Adenoviral TGF-β1- or Bleomycin-Induced Lung Fibrosis in Mice

Idiopathic pulmonary fibrosis (IPF) is an irreversible, age-related diffuse parenchymal lung disease of poorly defined etiology. Many patients with IPF demonstrate distinctive lymphocytic interstitial infiltrations within remodeled lung tissue with uncertain pathogenetic relevance. Histopathological examination of explant lung tissue of patients with IPF revealed accentuated lymphoplasmacellular accumulations in close vicinity to, or even infiltrating, remodeled lung tissue. Similarly, we found significant accumulations of B cells interfused with T cells within remodeled lung tissue in two murine models of adenoviral TGF-β1 or bleomycin (BLM)-induced lung fibrosis. Such B cell accumulations coincided with significantly increased lung collagen deposition, lung histopathology, and worsened lung function in wild-type (WT) mice. Surprisingly, B cell-deficient µMT knockout mice exhibited similar lung tissue remodeling and worsened lung function upon either AdTGF-β1 or BLM as for WT mice. Comparative transcriptomic profiling of sorted B cells collected from lungs of AdTGF-β1- and BLM-exposed WT mice identified a large set of commonly regulated genes, but with significant enrichment observed for Gene Ontology terms apparently not related to lung fibrogenesis. Collectively, although we observed B cell accumulations in lungs of IPF patients as well as two experimental models of lung fibrosis, comparative profiling of characteristic features of lung fibrosis between WT and B cell-deficient mice did not support a major involvement of B cells in lung fibrogenesis in mice.

Analysis of Janus tyrosine kinase phosphorylation and activation

Activation of Janus kinases (Jaks) occurs through autophosphorylation of key tyrosine residues located primarily within their catalytic domain. Phosphorylation of these tyrosine residues facilitates access of substrates to the active site and serves as an intrinsic indicator of Jak activation. Here, we describe the methods and strategies used for analyzing Jak phosphorylation and activation. Tyrosine-phosphorylated (active) Jaks are primarily detected from cell extracts using anti-phosphotyrosine-directed Western blot analysis of Jak-specific immunoprecipitates. Additionally, receptor pull-down and in vitro kinase assays can also be utilized to measure cellular Jak catalytic activity. In addition to tyrosine phosphorylation, recent evidence indicates Jaks can be serine phosphorylated upon cytokine stimulation, however the lack of commercially available antibodies to detect these sites has hindered their analysis by Western blot. However, phosphoamino acid analysis (PAA) has been employed to monitor Jak serine and threonine phosphorylation. Over the past decade, remarkable advances have been made in our understanding of Jak function and dysfunction, however much remains to be learned about their complex regulatory mechanisms.

Activation of the Janus Kinase 3-STAT5a Pathway After CD40 Triggering of Human Monocytes But Not of Resting B Cells

CD40/CD40 ligand interactions play a key role in the immune responses of B lymphocytes, monocytes, and dendritic cells. The signal transduction events triggered by cross-linking of the CD40 receptor have been widely studied in B cell lines, but little is known about signaling following CD40 stimulation of monocytes and resting tonsillar B cells. Therefore, we studied the CD40 pathway in highly purified human monocytes and resting B cells. After CD40 triggering, a similar activation of the NF-κB (but not of the AP-1) transcription factor complex occurred in both cell preparations. However, the components of the NF-κB complexes were different in monocytes and B cells, because p50 is part of the NF-κB complex induced by CD40 triggering in both monocytes and B cells, whereas p65 was only induced in B cells. In contrast, although the Janus kinase 3 tyrosine kinase was associated with CD40 molecules in both monocytes and resting B cells, Janus kinase 3 phosphorylation induction was observed only in CD40-activated monocytes, with subsequent induction of STAT5a DNA binding activity in the nucleus. These results suggest that the activation signals in human B cells and monocytes differ following CD40 stimulation. This observation is consistent with the detection of normal CD40-induced monocyte activation in patients with CD40 ligand+ hyper IgM syndrome in whom a defect in CD40-induced B cell activation has been reported.

IgE Hyperproduction Through Enhanced Tyrosine Phosphorylation of Janus Kinase 3 in NC/Nga Mice, a Model for Human Atopic Dermatitis

IgE hyperproduction frequently observed in patients with atopic dermatitis (AD) may greatly contribute to the pathogenesis of AD, but its mechanisms are still unclear. NC/Nga mice raised in nonsterile circumstances spontaneously suffered from AD-like skin lesions with elevation of plasma IgE levels. We investigated mechanisms of the IgE hyperproduction in NC/Nga mice. Splenic T cells from SPF NC/Nga mice had a level of CD40 ligand (CD40L) expression comparable to that of BALB/c mice. Although there was no difference in the expression of CD40 on B cells between NC/Nga and BALB/c mice, B cells of NC/Nga mice produced much more IgE in the presence of soluble CD40L and IL-4. The stimulation with CD40L and/or IL-4 resulted in tyrosine phosphorylation of Janus kinase 3 (JAK3) in B cells, which was more strongly inducible in NC/Nga mice than in BALB/c mice. In B cells isolated from PBMC of AD patients with high serum IgE levels, JAK3 was constitutively phosphorylated at the tyrosine residue, and its phosphorylation was enhanced by the treatment with CD40L and/or IL-4 as was that in splenic B cells of NC/Nga mice with dermatitis and high IgE levels. Thus, it is suggested that constitutive and enhanced JAK3 phosphorylation in B cells highly sensitive to CD40L and IL-4 may be attributable to IgE hyperproduction in NC/Nga mice and patients with AD.