The protein known as macrophage migration inhibitory factor (MIF) was one of the first cytokines to be discovered and was described 30 years ago to be a T-cellderived factor that inhibited the random migration of macrophages in vitro. A much broader role for MIF has emerged recently as a result of studies that have demonstrated it to be released from the anterior pituitary gland in vivo. MIF also is the first protein that has been identified to be secreted from monocytes/macrophages upon glucocorticoid stimulation. Once released, MIF acts to "override" or counter-regulate the suppressive effects of glucocorticoids on macrophage cytokine production. We report herein that MIF plays an important regulatory role in the activation of T cells induced by mitogenic or antigenic stimuli. Activated T cells produce MIF and neutralizing anti-MIF antibodies inhibit T-cell proliferation and interleukin 2 production in vitro, and suppress antigendriven T-cell activation and antibody production in vivo. T cells also release MIF in response to glucocorticoid stimulation and MIF acts to override glucocorticoid inhibition of T-cell proliferation and interleukin 2 and interferon y production. These studies indicate that MIF acts in concert with glucocorticoids to control T-cell activation and assign a previously unsuspected but critical role for MIF in antigenspecific immune responses.

Hypoxia has been reported to inhibit activity and expression of ion transporters of alveolar epithelial cells. This study extended those observations by investigating the mechanisms underlying inhibition of active Na transport across primary cultured adult rat alveolar epithelial cell monolayers grown on polycarbonate filters. Cell monolayers were exposed to normoxia and hypoxia (1.5% and 5% O(2), 5% CO(2)), and resultant changes in bioelectric properties [i.e., short-circuit current (I(sc)) and transepithelial resistance (R(t))] were measured in Ussing chambers. Results showed that I(sc) decreased with duration of exposure to hypoxia, while relatively little change was observed for R(t). In normoxia, amiloride inhibited approximately 70% of I(sc). The amiloride-sensitive portion of I(sc) decreased over time of exposure to hypoxia, whereas the magnitude of the amiloride-insensitive portion of I(sc) was not affected. Na pump capacity measured after permeabilization of the apical plasma membrane with amphotericin B decreased in monolayers exposed to 1.5% O(2) for 24 h, as did the capacity of amiloride-sensitive Na uptake measured after imposing an apical to basolateral Na gradient and permeabilization of the basolateral membrane. These results demonstrate that exposure to hypoxia inhibits alveolar epithelial Na reabsorption by reducing the rates of both apical amiloride-sensitive Na entry and basolateral Na extrusion.

CD8+ T cells are a major source of IFN-γ, a key effector cytokine in immune responses against many viruses and protozoa. Although the transcription factor T-bet is required for IFN-γ expression in CD4+ T cells, it is reportedly dispensable in CD8+ T cells, where the transcription factor Eomesodermin is thought to be sufficient. The diverse functions of IFN-γ are mediated through the IFN-γR and STAT1. In CD4+ T cells, STAT1 appears to be critical for the activation of T-bet and IFN-γ, suggesting an IFN-γ-dependent positive feedback loop. However, STAT1 can also be activated by other cytokines, including IL-27. In the present study we show that, in contrast to in vitro conditions and the prevailing paradigm, T-bet is critical for the in vivo IFN-γ production by CD8+ T cells upon infection of mice with diverse pathogens. Whereas IFN-γR signals are dispensable for the T-bet-dependent IFN-γ production, direct IL-27Rα signals are critical.

The expression of IFN-γ is a hallmark of Th1 cells and CD8+ effector T cells and is the signature cytokine of type 1 responses. However, it is not known whether T cells are homogeneous in their capacity to produce IFN-γ, whether this potential varies between tissues, and how it relates to the production of other effector molecules. In the present study we used bicistronic IFN-γ-enhanced yellow fluorescent protein (IFN-γ-eYFP) reporter mice (Yeti) and MHC class I tetramers to directly quantify IFN-γ expression at the single cell level. The eYFP fluorescence of Th1 cells and CD8+ effector T cells was broadly heterogeneous even before cell division and correlated with both the abundance of IFN-γ transcripts and the secretion of IFN-γ upon stimulation. CD4+ and CD8+ T cells of influenza-infected mice revealed a similarly heterogeneous IFN-γ expression, and eYFPhigh cells were only found in the infected lung. Ag-specific T cells were in all examined tissues eYFP+, but also heterogeneous in their reporter fluorescence, and eYFPhigh cells were also restricted to the infected lung. A similar heterogeneity was observed in Toxoplasma gondii-infected animals, but eYFPhigh cells were restricted to different tissues. Highly eYFP fluorescent cells produced elevated levels of proinflammatory cytokines and chemokines in addition to IFN-γ, suggesting their coregulated expression as a functional unit in highly differentiated effector T cells.

Taken together our data suggest that live BCG>hk-BCG>CpG-ODN >PPD are effective in suppressing allergen-induced Th2 responses. The degree of suppression and the component of the Th2 response affected (airway inflammation vs. the production of allergen-specific IgE and IgG1) were dependent upon the adjuvant used and how it was applied. Our results contribute to the design of novel vaccines protecting humans from developing allergic disorders.