Hypersensitivity pneumonitis (HP) is an inflammatory lung disease characterized by a diffuse mononuclear cell infiltrate in the lung that can progress to pulmonary fibrosis with chronic exposure to an inhaled Ag. We previously reported that C57BL/6 mice repeatedly exposed to the ubiquitous microorganism Bacillus subtilis develop mononuclear infiltrates in the lung that contain Vγ6/Vδ1+ γδ T cells. In the absence of this T cell subset, mice treated with B. subtilis had significantly increased collagen deposition in the lung, suggesting a regulatory role for Vγ6/Vδ1+ γδ T cells. To further investigate the role of Vγ6/Vδ1+ γδ T cells in B. subtilis-induced lung fibrosis, we exposed transgenic Vγ6/Vδ1 mice to this microorganism and found decreased collagen content in the lung compared with wild-type C57BL/6 mice. Cytokine analysis of lung homogenates from wild-type C57BL/6 mice demonstrated increased IL-17A concentrations with repeated exposure to B. subtilis. In the absence of IL-17 receptor signaling, IL-17ra−/− mice had delayed clearance of B. subtilis with increased lung inflammation and fibrosis. Although IL-17A was predominantly expressed by Vγ6/Vδ1+ T cells, a compensatory increase in IL-17A expression by CD4+ T cells was seen in the absence of γδ T cells that resulted in similar levels of IL-17A in the lungs of TCRδ−/− and wild-type C57BL/6 mice. In combination, our data suggest an important role for IL-17A-expressing T lymphocytes, both γδ and αβ T cells, in eliminating this microorganism that prevents excessive inflammation and eventual lung fibrosis in this murine model of B. subtilis-induced hypersensitivity pneumonitis.

Biliary atresia (BA) is a progressive, inflammatory cholangiopathy that culminates in fibrosis of extrahepatic and intrahepatic bile ducts. A leading theory on the pathogenesis of BA is that the bile duct damage is initiated by a virus infection, followed by a bile duct-targeted autoimmune response. One mechanism of autoimmunity entails diminished number or function of regulatory T cells (Tregs). The aim of this study was to identify potential virus-specific liver T cells from infants with BA at the time of diagnosis, implicating the virus involved in early bile duct damage. A subaim was to determine if presence of virus infection was associated with quantitative changes in Tregs. Results: Liver T cells from BA and control patients were cultured with antigen presenting cells in the presence of a variety of viral or control proteins. 56% of BA patients had significant increases in IFN-γ-producing liver T cells in response to cytomegalovirus (CMV), compared to minimal BA responses to other viruses or the control group CMV response. In addition, a positive correlation between BA plasma CMV IgM and liver T cell CMV reactivity was identified. Investigation of peripheral blood Tregs revealed significant deficits in Tregs frequencies in BA compared to controls, with marked deficits in those BA patients who were positive for CMV. Conclusions: Liver T cell responses to CMV were identified in the majority of BA patients at diagnosis, suggesting perinatal CMV infection as a plausible initiator of bile duct damage. Deficiency of Tregs in BA implies decreased inhibition of inflammation and autoreactivity, potentially allowing for exaggerated bile duct injury.

Beryllium exposure in the workplace can result in chronic beryllium disease, a granulomatous lung disorder characterized by CD4+ T cell alveolitis and progressive lung fibrosis. A large number of the CD4+ T cells recruited to the lung in chronic beryllium disease recognize beryllium in an Ag-specific manner and express Th1-type cytokines following T cell activation. Beryllium-responsive CD4+ T cells in the bronchoalveolar lavage (BAL) express an effector memory T cell phenotype and recognize beryllium in a CD28-independent manner. In this study, we show that the majority of beryllium-responsive CD4+ T cells in BAL have lost CD27 expression, whereas a subset of beryllium-responsive cells in blood retains expression of this costimulatory molecule. In addition, loss of CD27 on BAL CD4+ T cells inversely correlates with markers of lung inflammation. A small population of BAL CD4+ T cells retains CD27 expression, and these CD4+CD27+ T cells contain the FoxP3-expressing, naturally occurring regulatory T (Treg) cell subset. Coexpression of CD27 and CD25 identifies the majority of FoxP3-expressing Treg cells in blood and BAL, and these cells express potent suppressor function. Taken together, these findings suggest that CD27 is differentially expressed between effector T cells from the inflamed lung and can be used in conjunction with CD25 to isolate Treg cells and assess their functional capacity in an ongoing adaptive immune response in a target organ.

Rationale: Chronic beryllium disease (CBD) is a CD4 1 T cell-mediated disorder characterized by persistent lung inflammation. Naturally occurring regulatory T (T reg ) cells modulate adaptive immune responses. The role of this T-cell subset in beryllium-induced lung disease is unknown. Objectives: The aim of this study was to determine whether dysfunctional T reg cells in the lung contribute to the ''unchecked'' inflammatory response that characterizes CBD. Methods: Using blood and bronchoalveolar lavage (BAL) cells from normal control subjects and individuals with beryllium-induced disease, we determined the frequency and function of naturally occurring T reg cells. Measurements and Main Results: A significantly decreased percentage and expression of FoxP3 in BAL CD4 1 T cells from CBD patients compared with beryllium-sensitized subjects was seen, and the percentage of FoxP3-expressing CD4 1 T reg cells in BAL inversely correlated with disease severity. In contrast to blood T reg cells derived from beryllium-sensitized subjects and patients with CBD that completely suppressed blood responder T-cell proliferation, BAL FoxP3-expressing T reg cells from patients with CBD are unable to suppress anti-CD3-mediated BAL T-cell proliferation. Mixing studies showed that blood T reg cells are capable of suppressing autologous BAL responder T cells. Conversely, BAL CD4 1 T reg cells are incapable of suppressing blood T cells, confirming that the failure of BAL T reg cells to suppress T-cell proliferation is caused by a dysfunctional T reg cell subset and not by resistance of BAL effector T cells to suppression. Conclusions: These findings suggest that the deficient and dysfunctional T reg cells in the lung of patients with CBD contribute to the persistent inflammatory response in this disease.