Interactions between major histocompatibility complex (MHC) molecules and the CD4 or CD8 coreceptors have a major role in intrathymic T-cell selection. On mature T cells, each of these two glycoproteins is associated with a class-specific bias in MHC molecule recognition by the T-cell receptor. CD4+ T cells respond to antigen in association with MHC class II molecules and CD8+ T cells respond to antigen in association with MHC class I molecules. Physical interaction between the CD4/MHC class II molecules and CD8/MHC class I molecules has been demonstrated by cell adhesion assay, and a binding site for CD8 on class I has been identified. Here we demonstrate that a region of the MHC class II beta-chain beta 2 domain, structurally analogous to the CD8-binding loop in the MHC class I alpha 3 domain, is critical for function with both mouse and human CD4.

The causative agent of anthrax, Bacillus anthracis, produces two toxins that contribute in part to its virulence. Lethal toxin is a metalloprotease that cleaves upstream mitogen-activated protein kinase kinases. Edema toxin is a calmodulin-dependent adenylate cyclase. Previous studies demonstrated that the anthrax toxins are important immunomodulators that promote immune evasion of the bacterium by suppressing activation of macrophages and dendritic cells. Here we showed that injection of sublethal doses of either lethal or edema toxin into mice directly inhibited the subsequent activation of T lymphocytes by T-cell receptor-mediated stimulation. Lymphocytes were isolated from toxin-injected mice after 1 or 4 days and stimulated with antibodies against CD3 and CD28. Treatment with either toxin inhibited the proliferation of T cells. Injection of lethal toxin also potently inhibited cytokine secretion by stimulated T cells. The effects of edema toxin on cytokine secretion were more complex and were dependent on the length of time between the injection of edema toxin and the isolation of lymphocytes. Treatment with lethal toxin blocked multiple kinase signaling pathways important for T-cell receptor-mediated activation of T cells. Phosphorylation of the extracellular signalregulated kinase and the stress-activated kinase p38 was significantly decreased. In addition, phosphorylation of the serine/threonine kinase AKT and of glycogen synthase kinase 3 was inhibited in T cells from lethal toxin-injected mice. Thus, anthrax toxins directly act on T lymphocytes in a mouse model. These findings are important for future anthrax vaccine development and treatment.Anthrax is caused by Bacillus anthracis, a large, rod-shaped, spore-forming, gram-positive bacterium (27). Stable B. anthracis spores form the basis of potential biological or bioterrorism weapons. The virulence of B. anthracis is dependent on the genes carried by two plasmids, pXO1 and pXO2. The genes for the synthesis of an antiphagocytic poly-␥-D-glutamic acid capsule are encoded by pXO2. Plasmid pXO1 contains three genes, pag, lef, and cya, which encode protective antigen (PA), lethal factor (LF), and edema factor (EF), respectively (26). These three proteins form two toxins, edema toxin (EdTx; PA plus EF) and lethal toxin (LeTx; PA plus LF). PA is the receptor-binding component of the anthrax toxins and mediates their entry into host cells. Once PA binds to the receptor, it is cleaved at the N-terminal region by a host cell surface protease (3). The resulting 63-kDa protein heptamerizes and forms a ring structure with competitive binding sites for three molecules of LF and/or EF (28). The toxin complex is then taken up via receptor-mediated endocytosis (5).The cellular receptors for PA are expressed on a wide variety of cell lines and tissues, including peripheral blood leukocytes, at moderate to low levels (3, 43). EF is a calmodulin-dependent adenylate cyclase that forms cyclic AMP (cAMP) from ATP (23), and LF is a zinc metalloprotease with mitogenactivated...

A pathological hallmark of asthma is chronic injury and repair, producing dysfunction of the epithelial barrier function. In this setting, increased oxidative stress, growth factor- and cytokine stimulation, together with extracellular matrix contact produces transcriptional reprogramming of the epithelial cell. This process results in epithelial-mesenchymal transition (EMT), a cellular state associated with loss of epithelial polarity, expression of mesenchymal markers, enhanced mobility and extracellular matrix remodeling. As a result, the cellular biology of the EMT state produces characteristic changes seen in severe, refractory asthma: myofibroblast expansion, epithelial trans-differentiation and subepithelial fibrosis. EMT also induces profound changes in epithelial responsiveness that affects innate immune signaling that may have impact on the adaptive immune response and effectiveness of glucocorticoid therapy in severe asthma. We discuss how this complex phenotype is beginning to be understood using systems biology-level approaches through perturbations coupled with high throughput profiling and computational modeling. Understanding the distinct changes induced by EMT at the systems level may provide translational strategies to reverse the altered signaling and physiology of refractory asthma.