Cutting Edge: Tissue Antigen Expression Levels Fine-Tune T Cell Differentiation Decisions In Vivo

Immune homeostasis in peripheral tissues is, to a large degree, maintained by the differentiation and action of regulatory T cells (Treg) specific for tissue Ags. Using a novel mouse model, we have studied the differentiation of naive CD4⁺ T cells into Foxp3⁺ Treg in response to a cutaneous Ag (OVA). We found that expression of OVA resulted in fatal autoimmunity and in prevention of peripheral Treg generation. Inhibiting mTOR activity with rapamycin rescued the generation of Foxp3⁺ T cells. When we varied the level of Ag expression to modulate TCR signaling, we found that low Ag concentrations promoted the generation of Foxp3⁺ T cells, whereas high levels expanded effector T cells and caused severe autoimmunity. Our findings indicate that the expression level of tissue Ag is a key determinant of the balance between tissue-reactive effector and peripheral Foxp3⁺ T cells, which determines the choice between tolerance and autoimmunity.

Anti-Interleukin-6 Promotes Allogeneic Bone Marrow Engraftment and Prolonged Graft Survival in an Irradiation-Free Murine Transplant Model

Transfer of recipient regulatory T cells (Tregs) induces mixed chimerism and tolerance in an irradiation-free bone marrow (BM) transplantation (BMT) model involving short-course co-stimulation blockade and mTOR inhibition. Boosting endogenous Tregs pharmacologically in vivo would be an attractive alternative avoiding the current limitations of performing adoptive cell therapy in the routine clinical setting. Interleukin-6 (IL-6) potently inhibits Treg differentiation and its blockade was shown to increase Treg numbers in vivo. Therefore, we investigated whether IL-6 blockade can replace adoptive Treg transfer in irradiation-free allogeneic BMT. Treatment with anti-IL-6 instead of Treg transfer led to multi-lineage chimerism (persisting for ~12 weeks) in recipients of fully mismatched BM and significantly prolonged donor skin (MST 58 days) and heart (MST > 100 days) graft survival. Endogenous Foxp3⁺ Tregs expanded in anti-IL-6-treated BMT recipients, while dendritic cell (DC) activation and memory CD8⁺ T cell development were inhibited. Adding anti-IL-17 to anti-IL-6 treatment increased Treg frequencies, but did not further prolong donor skin graft survival significantly. These results demonstrate that IL-6 blockade promotes BM engraftment and donor graft survival in non-irradiated recipients and might provide an alternative to Treg cell therapy in the clinical setting.

Hydration study of homopolypeptides by (2)H NMR

Deuteron T(1) and T(2) was studied as a function of hydration in homopolyglycine (PG) and homopolyproline (PP). Water deuteron relaxation rates in PG conform to a hydration model involving two types of primary hydration sites where water is directly bonded to the polymer. Once these sites are filled, additional water only bonds to water molecules at the primary sites and in so doing affect their dynamics. PP exhibits an anomalous T(1) and T(2) hydration dependence which has been interpreted in terms of a cooperative water molecule-PP molecule helical conformational rearrangement which occurs once a certain hydration level is reached. The proposal of a water-PP structure is tested using molecular dynamics simulations.

Cross-relaxation bottleneck in water–lysozyme proton magnetization exchange

The proton spin-lattice relaxation parameters in natural and deuterated lysozyme solutions have been measured as a function of temperature (0-50 degrees C). The variation of the apparent magnitudes of the water proton magnetizations in the solutions with temperature indicates that magnetic coupling mixes protein and water proton magnetizations. The results are consistent with an exchange cross-relaxation model (Hills, B. P., Mol Phys 1992, 76, 489-508) in which the cross-relaxation acts between the labile and nonlabile protons, rather than between water and protein protons. Although this cross-relaxation pathway clearly affects the observed magnetization fractions in this protein solution, its influence on the relaxation rates is less apparent.

Proton spin-spin relaxation study of hydration of a model nanopore

The hydration pattern of controlled pore glass, with pore diameter of 237 A, was investigated using nuclear magnetic resonance. Water proton spin-spin relaxation decay curves were monitored and modeled as two-component exponential decays as a function of hydration. The results are consistent with a geometric model involving a surface water layer and a bulk-like liquid fraction in the form of a plug. The amount of surface water increases as the sample hydrates, until hydration reached approximately a monolayer, at which point a water plug starts to form in the pore, and grow in length at the expense of the surface layer. The results are also analyzed in terms of, and compared to, a recently developed puddle pore-filling model [S.G. Allen, et al. J. Chem. Phys. 106 (1997) 7802-7809].

Cloning and expression of a cellular high density lipoprotein-binding protein that is up-regulated by cholesterol loading of cells

Plasma membranes of cultured cells contain high affinity receptors for high density lipoprotein (HDL) that appear to mediate removal of excess intracellular cholesterol. Recent studies using ligand blot analysis have identified a 110-kDa membrane protein which has features predicted for an HDL receptor, in that it preferentially binds HDL apolipoproteins and undergoes up-regulation in response to cholesterol loading of cells. In this study, we isolated a cDNA clone from an expression library using an antibody raised against partially purified 110-kDa HDL-binding protein. This clone encodes a novel cell protein, designated HBP, comprised mostly of 14 imperfect tandem repeats of approximately 70 amino acids in length. Each repeat appears to contain two amphipathic helices. Expression of HBP in cultured cells was increased severalfold when cells were loaded with cholesterol, as evident by increases in both HBP mRNA and membrane-associated protein. Overexpression of HBP in mammalian cell transfectants was associated with higher HDL binding to isolated cell protein and with modest increases in HDL binding to the cell surface. Proteins identified by ligand blot analysis had lower apparent M(r) than the primary HBP gene product and varied in M(r) and in HDL binding activity between cell types, suggesting that HBP undergoes cell-specific processing. These results provide preliminary evidence that HBP is a component of a cellular pathway that facilitates removal of excess cholesterol from cells, perhaps through its interaction with HDL. However, the predicted structure of HBP does not conform to that of any known receptor, suggesting that it does not function as a classic plasma membrane receptor.

Exercise and sudden death

Sudden death during exercise is rare, but limited data suggest that vigorous physical activity is associated with an increased risk for this event, particularly in individuals with overt cardiac disease or a high coronary risk profile. The mechanism of exercise-associated sudden death is usually a lethal arrhythmia; however, this may vary depending on the underlying cardiovascular disease. In the great majority of cases, cardiovascular disease is present in persons who die during exercise. In young individuals (less than 35 years old) hypertrophic cardiomyopathy and congenital coronary anomalies are the most common conditions, whereas older victims usually have coronary artery disease. Cardiac disease is typically unrecognized prior to death in young persons; in the older population, most have overt coronary disease or recognizable coronary risk factors. Screening asymptomatic individuals to identify increased risk of a cardiac event during exercise presents major problems in terms of logistics, expense, and accuracy, but careful evaluation, including exercise testing, is mandatory before a program of increased activity in patients with overt cardiac disease. In other cases, the extent of any evaluation must be determined on an individual basis.

The "pedicle flap": a technique for complete excision of benign salivary gland tumors of the palate

Morphology and growth pattern of the pleomorphic adenoma are discussed. The relationship between these factors and recurrence is examined. A new technique for excision is also described. This technique is particularly useful for those tumors that extend into the soft palate.