High dose bee venom exposure in beekeepers by natural bee stings represents a model to understand mechanisms of T cell tolerance to allergens in healthy individuals. Continuous exposure of nonallergic beekeepers to high doses of bee venom antigens induces diminished T cell–related cutaneous late-phase swelling to bee stings in parallel with suppressed allergen-specific T cell proliferation and T helper type 1 (Th1) and Th2 cytokine secretion. After multiple bee stings, venom antigen–specific Th1 and Th2 cells show a switch toward interleukin (IL) 10–secreting type 1 T regulatory (Tr1) cells. T cell regulation continues as long as antigen exposure persists and returns to initial levels within 2 to 3 mo after bee stings. Histamine receptor 2 up-regulated on specific Th2 cells displays a dual effect by directly suppressing allergen-stimulated T cells and increasing IL-10 production. In addition, cytotoxic T lymphocyte–associated antigen 4 and programmed death 1 play roles in allergen-specific T cell suppression. In contrast to its role in mucosal allergen tolerance, transforming growth factor β does not seem to be an essential player in skin-related allergen tolerance. Thus, rapid switch and expansion of IL-10–producing Tr1 cells and the use of multiple suppressive factors represent essential mechanisms in immune tolerance to a high dose of allergens in nonallergic individuals.

These data suggest that T regulatory cells may contribute to the suppression of allergic diseases by suppression of IgE and induction of IgG4, whereas IgA production is enhanced by B-cell activation via TLR7 and TLR9.

Forkhead box P3 (FOXP3)+CD4+CD25+ inducible regulatory T (iT reg) cells play an important role in immune tolerance and homeostasis. In this study, we show that the transforming growth factor-β (TGF-β) induces the expression of the Runt-related transcription factors RUNX1 and RUNX3 in CD4+ T cells. This induction seems to be a prerequisite for the binding of RUNX1 and RUNX3 to three putative RUNX binding sites in the FOXP3 promoter. Inactivation of the gene encoding RUNX cofactor core-binding factor-β (CBFβ) in mice and small interfering RNA (siRNA)-mediated suppression of RUNX1 and RUNX3 in human T cells resulted in reduced expression of Foxp3. The in vivo conversion of naive CD4+ T cells into Foxp3+ iT reg cells was significantly decreased in adoptively transferred CbfbF/F CD4-cre naive T cells into Rag2−/− mice. Both RUNX1 and RUNX3 siRNA silenced human T reg cells and CbfbF/F CD4-cre mouse T reg cells showed diminished suppressive function in vitro. Circulating human CD4+ CD25high CD127− T reg cells significantly expressed higher levels of RUNX3, FOXP3, and TGF-β mRNA compared with CD4+CD25− cells. Furthermore, FOXP3 and RUNX3 were colocalized in human tonsil T reg cells. These data demonstrate Runx transcription factors as a molecular link in TGF-β–induced Foxp3 expression in iT reg cell differentiation and function.

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A broad spectrum of beneficial effects has been ascribed to creatine (Cr), phosphocreatine (PCr) and their cyclic analogues cyclo-(cCr) and phospho-cyclocreatine (PcCr). Cr is widely used as nutritional supplement in sports and increasingly also as adjuvant treatment for pathologies such as myopathies and a plethora of neurodegenerative diseases. Additionally, Cr and its cyclic analogues have been proposed for anti-cancer treatment. The mechanisms involved in these pleiotropic effects are still controversial and far from being understood. The reversible conversion of Cr and ATP into PCr and ADP by creatine kinase, generating highly diffusible PCr energy reserves, is certainly an important element. However, some protective effects of Cr and analogues cannot be satisfactorily explained solely by effects on the cellular energy state. Here we used mainly liposome model systems to provide evidence for interaction of PCr and PcCr with different zwitterionic phospholipids by applying four independent, complementary biochemical and biophysical assays: (i) chemical binding assay, (ii) surface plasmon resonance spectroscopy (SPR), (iii) solid-state 31P-NMR, and (iv) differential scanning calorimetry (DSC). SPR revealed low affinity PCr/phospholipid interaction that additionally induced changes in liposome shape as indicated by NMR and SPR. Additionally, DSC revealed evidence for membrane packing effects by PCr, as seen by altered lipid phase transition. Finally, PCr efficiently protected against membrane permeabilization in two different model systems: liposome-permeabilization by the membrane-active peptide melittin, and erythrocyte hemolysis by the oxidative drug doxorubicin, hypoosmotic stress or the mild detergent saponin. These findings suggest a new molecular basis for non-energy related functions of PCr and its cyclic analogue. PCr/phospholipid interaction and alteration of membrane structure may not only protect cellular membranes against various insults, but could have more general implications for many physiological membrane-related functions that are relevant for health and disease.