Bronchial asthma is a chronic disease characterized by reversible airway obstruction, mucus production, and bronchial hyperresponsiveness (BHR). Although Th2 cell-mediated eosinophilic inflammation is an important disease mechanism in the majority of patients with bronchial asthma, recent studies suggest the possible development of Th2-independent airway inflammation and BHR. These non-Th2 endotype patients seem to consist of multiple subgroups, and often do not respond to inhaled corticosteroids. Therefore, to understand the pathogenesis of asthma, it is important to characterize these non-Th2 subgroups. Recently, we demonstrated that Th9 cells induce eosinophil infiltration and eosinophil-independent BHR, and Th9 cells-mediated BHR may be resistant to glucocorticoid. In this review, we summarize the contribution of several T cell subsets in the development of bronchial asthma and introduce our recent study demonstrating Th9 cell-mediated and eosinophil-independent BHR.

Reduced responsiveness to corticosteroid therapy is a major problem for patients with severe asthma. Although Th9 cells, along with Th2 cells, facilitate antigen-induced airway eosinophilia and bronchial hyperresponsiveness (BHR), the sensitivity of Th9 cell-mediated responses to steroid therapy remains unknown. In this study, we investigated the effect of dexamethasone (Dex) on antigen-induced airway inflammation in Th9 cell-transferred mice. Ovalbumin (OVA)-specific Th2 and Th9 cells were polarized from the CD4+ T cells of DO11.10/RAG-2-/- mice. BALB/c mice were adoptively transferred with Th2 or Th9 cells and challenged with OVA. Dex treatment was performed twice, at 1 h before and at 24 h after the OVA challenge. Following treatment, the number of inflammatory cells in the bronchoalveolar lavage fluid and the bronchial responsiveness to inhaled methacholine were determined. In both the Th2 and Th9 cell-transferred mice, substantial accumulation of eosinophils in the lungs and BHR were induced by challenge with the specific antigen. In the Th2 cell-transferred mice, these responses were significantly diminished by Dex treatment. In contrast, neither cellular infiltration nor BHR was affected by Dex treatment in the Th9 cell-transferred mice, although the Th9 cells substantially expressed glucocorticoid receptor α. Accordingly, antigen-induced interleukin-9 expression in the Th9 cells was attenuated by Dex treatment at least in vitro. Antigen-induced lung infiltration of infused Th2 cells but not Th9 cells was significantly suppressed by Dex. In contrast to Th2-mediated responses, Th9-mediated airway inflammation was not affected by Dex. Th9 cells might be involved in the developmental mechanisms of steroid-resistant asthma.

Airway accumulation of eosinophils and bronchial hyperresponsiveness (BHR) are prominent features of bronchial asthma, though the contribution of eosinophils to the development of BHR is controversial. Similar to Th2 cell-mediated pathology, Th9 cells, characterized by IL-9-producing activity, have been demonstrated to induce airway eosinophilia and BHR. In this study, we investigated the role of eosinophils in Th9-mediated BHR by employing Th9 cell-transferred murine airway inflammation model. Ovalbumin (OVA)-specific Th2 and Th9 cells were differentiated from CD4(+) T cells of DO11.10/RAG-2(-/-) mice in vitro and cytokine-producing activity of those cells was examined. BALB/c mice were adoptively transferred with Th2 or Th9 cells and challenged with OVA. Then, the number of inflammatory cells in bronchoalveolar lavage fluid and bronchial responsiveness to inhaled methacholine were determined. Both in Th2 and Th9 cell-transferred mice, substantial accumulation of eosinophils in the lungs and BHR were induced by challenge with specific antigen. Nevertheless, an essential and dispensable role of eosinophils in Th2- and Th9-mediated BHR, respectively, was demonstrated by employing eosinophil-deficient mice. The neutralization of IL-9 as well as deficiency of IL-10 in the donor cells did not affect Th9-mediated BHR. In contrast to Th2-mediated and eosinophil-dependent BHR, Th9 could induce BHR independently from eosinophils and its characteristic cytokines, IL-9 and IL-10.

Histamine, a prominent mediator of the symptoms and pathogenesis of allergic diseases, is produced not only by mast cells and basophils via the classical degranulation process but also by other immune cells including T cells via a neosynthesis process. Interestingly, T cells produce and are affected by histamine. Various T cell functions are also regulated by histamine via H1, H2, and H4 receptors. We recently demonstrated that T cells induce massive allergic inflammation without assistance from the immunoglobulin E (IgE)/mast cell-dependent pathway, and histamine may be involved in the development of allergic diseases via the functional modulation of and production by T cells. Based on these reports, we propose a new role of histamine and T cells in allergic diseases that differs from the established paradigm. Aside from our recent study showing the downregulation of regulatory T (Treg) cells by histamine via H1R and H4R in a murine allergic dermatitis model, the detailed roles of histamine and T cells in histamine production, expression of histamine receptors, and histamine-mediated activity for a series of T cell subsets remain to be elucidated.

Background: Human cytomegalovirus (CMV) is a major pathogen that poses significant risks to immunocompromised individuals and neonates. The tegument protein pp71, encoded by the UL82 gene, plays a pivotal role in initiating viral lytic replication and evading host immune responses. Despite its clinical relevance, standardized monoclonal antibodies (mAbs) for pp71 remain limited, prompting the need to expand the available repertoire of antibodies targeting this critical protein. Methods: In this study, we constructed a diverse human single-chain variable fragment (scFv) library using RNA derived from the B cells of four healthy donors. The library was expressed in Saccharomyces cerevisiae, and iterative rounds of magnetic-activated cell sorting (MACS) were performed against recombinant pp71. Clonal enrichment was monitored using flow cytometry. Results: Among the isolated clones, one designated ID2 exhibited high sensitivity and specificity for pp71, as demonstrated by flow cytometry, immunofluorescence, an enzyme-linked immunosorbent assay (ELISA), and biolayer interferometry (BLI). Conclusions: Collectively, these findings establish a novel pp71-specific mAb and underscore the utility of yeast surface display combined with MACS for expanding the antibody toolkit available for CMV research and diagnostics.