Abdallah Elkhal

WIP is a chaperone for Wiskott–Aldrich syndrome protein (WASP)

Wiskott–Aldrich syndrome protein (WASP) is in a complex with WASP-interacting protein (WIP). WASP levels, but not mRNA levels, were severely diminished in T cells from WIP−/− mice and were increased by introduction of WIP in these cells. The WASP binding domain of WIP was shown to protect WASP from degradation by calpain in vitro. Treatment with the proteasome inhibitors MG132 and bortezomib increased WASP levels in T cells from WIP−/− mice and in T and B lymphocytes from two WAS patients with missense mutations (R86H and T45M) that disrupt WIP binding. The calpain inhibitor calpeptin increased WASP levels in activated T and B cells from the WASP patients, but not in primary T cells from the patients or from WIP−/− mice. Despite its ability to increase WASP levels proteasome inhibition did not correct the impaired IL-2 gene expression and low F-actin content in T cells from the R86H WAS patient. These results demonstrate that WIP stabilizes WASP and suggest that it may also be important for its function.

Purinergic Signaling: A Fundamental Mechanism in Neutrophil Activation

Neutrophil activation by infectious and inflammatory signals requires ATP release and its feedback through purinergic receptors. Feedback for Function Neutrophils migrate to sites of infection, where they kill pathogens by processes such as phagocytosis and the release of reactive oxygen species. However, activated neutrophils can also result in tissue damage and inflammatory diseases in the host; thus, a better understanding of the mechanisms that regulate neutrophil activation could help in the development of therapies that could curb their destructive side effects. Chen et al. found that neutrophils responded to a range of infectious and inflammatory signals by releasing adenosine triphosphate (ATP). In addition to its role as a cellular energy source, ATP and its metabolites function as intercellular signaling molecules by stimulating purinergic receptors. The authors found that stimulation of formyl peptide receptors (FPRs) on neutrophils triggered the release, through pannexin-1 hemichannels, of ATP that signaled in an autocrine fashion through P2Y2 receptors. Moreover, this autocrine signal was required for neutrophil activation. In addition, mice deficient in P2Y2 receptors were less capable of clearing bacteria than were their wild-type counterparts. Together, these data suggest that feedback signaling by ATP released by neutrophils contributes to their activation. Efficient activation of neutrophils is a key requirement for effective immune responses. We found that neutrophils released cellular adenosine triphosphate (ATP) in response to exogenous stimuli such as formylated bacterial peptides and inflammatory mediators that activated Fcγ, interleukin-8, C5a complement, and leukotriene B4 receptors. Stimulation of the formyl peptide receptor (FPR) led to ATP release through pannexin-1 (panx1) hemichannels, and FPRs colocalized with P2Y2 nucleotide receptors on the cell surface to form a purinergic signaling system that facilitated neutrophil activation. Disruption of this purinergic signaling system by inhibiting or silencing panx1 hemichannels or P2Y2 receptors blocked neutrophil activation and impaired innate host responses to bacterial infection. Thus, purinergic signaling is a fundamental mechanism required for neutrophil activation and immune defense.

Vaccinia virus inoculation in sites of allergic skin inflammation elicits a vigorous cutaneous IL-17 response

Eczema vaccinatum (EV) is a complication of smallpox vaccination occurring in patients with atopic dermatitis. In affected individuals, vaccinia virus (VV) spreads through the skin, resulting in large primary lesions and satellite lesions, and infects internal organs. BALB/c mice inoculated with VV at sites of Th2-biased allergic skin inflammation elicited by epicutaneous ovalbumin (OVA) sensitization exhibited larger primary lesions that were erosive, more satellite lesions, and higher viral loads in skin and internal organs than mice inoculated in saline-exposed skin, unsensitized skin, or skin sites with Th1-dominant inflammation. VV inoculation in OVA-sensitized skin induced marked local expression of IL-17 transcripts and massive neutrophil infiltration compared to VV inoculation in saline-exposed skin. Treatment with anti-IL-17 decreased the size of primary lesions, numbers of satellite lesions, and viral loads. Addition of IL-17 promoted VV replication in skin explants. These results suggest that IL-17 may be a potential therapeutic target in EV.

Epicutaneous challenge of orally immunized mice redirects antigen-specific gut-homing T cells to the skin

Patients with atopic dermatitis (AD) often suffer from food allergy and develop flares upon skin contact with food allergens. However, it is unclear whether T cells sensitized to allergens in the gut promote this skin inflammation. To address this question, we orally immunized WT mice and mice lacking the skin-homing chemokine receptor Ccr4 (Ccr4-/- mice) with OVA and then challenged them epicutaneously with antigen. Allergic skin inflammation developed in the WT mice but not in the mutants and was characterized by epidermal thickening, dermal infiltration by eosinophils and CD4+ T cells, and upregulation of Th2 cytokines. T cells purified from mesenteric lymph nodes (MLNs) of orally immunized WT mice transferred allergic skin inflammation to naive recipients cutaneously challenged with antigen, but this effect was lost in T cells purified from Ccr4-/- mice. In addition, the ability of adoptively transferred OVA-activated T cells to home to the skin following cutaneous OVA challenge was ablated in mice that lacked lymph nodes. These results indicate that cutaneous exposure to food antigens can reprogram gut-homing effector T cells in LNs to express skin-homing receptors, eliciting skin lesions upon food allergen contact in orally sensitized AD patients.

Eosinophil-derived leukotriene C4 signals via type 2 cysteinyl leukotriene receptor to promote skin fibrosis in a mouse model of atopic dermatitis

Atopic dermatitis (AD) skin lesions exhibit epidermal and dermal thickening, eosinophil infiltration, and increased levels of the cysteinyl leukotriene (cys-LT) leukotriene C4 (LTC4). Epicutaneous sensitization with ovalbumin of WT mice but not ΔdblGATA mice, the latter of which lack eosinophils, caused skin thickening, collagen deposition, and increased mRNA expression of the cys-LT generating enzyme LTC4 synthase (LTC4S). Skin thickening and collagen deposition were significantly reduced in ovalbumin-sensitized skin of LTC4S-deficient and type 2 cys-LT receptor (CysLT2R)–deficient mice but not type 1 cys-LT receptor (CysLT1R)-deficient mice. Adoptive transfer of bone marrow-derived eosinophils from WT but not LTC4S-deficient mice restored skin thickening and collagen deposition in epicutaneous-sensitized skin of ΔdblGATA recipients. LTC4 stimulation caused increased collagen synthesis by human skin fibroblasts, which was blocked by CysLT2R antagonism but not CysLT1R antagonism. Furthermore, LTC4 stimulated skin fibroblasts to secrete factors that elicit keratinocyte proliferation. These findings establish a role for eosinophil-derived cys-LTs and the CysLT2R in the hyperkeratosis and fibrosis of allergic skin inflammation. Strategies that block eosinophil infiltration, cys-LT production, or the CysLT2R might be useful in the treatment of AD.

Autonomous vascular networks synchronize GABA neuron migration in the embryonic forebrain

GABA neurons, born in remote germinative zones in the ventral forebrain (telencephalon), migrate tangentially in two spatially distinct streams to adopt their specific positions in the developing cortex. The cell types and molecular cues that regulate this divided migratory route remains to be elucidated. Here we show that embryonic vascular networks are strategically positioned to fulfill the task of providing support as well as critical guidance cues that regulate the divided migratory routes of GABA neurons in the telencephalon. Interestingly, endothelial cells of the telencephalon are not homogeneous in their gene expression profiles. Endothelial cells of the periventricular vascular network have molecular identities distinct from those of the pial network. Our data suggest that periventricular endothelial cells have intrinsic programs that can significantly mold neuronal development and uncovers new insights into concepts and mechanisms of CNS angiogenesis from both developmental and disease perspectives.

Vascularized composite allotransplantation: current standards and novel approaches to prevent acute rejection and chronic allograft deterioration.

The advent of more potent immunosuppressants led to the first successful human upper extremity transplantation in 1998. At this time, >100 upper extremity transplants, 30 face transplants, and a variety of other vascularized composite allotransplantation (VCA) procedures have been performed around the world. VCA recipients present unique challenges for transplantation. The incidence of acute rejection exceeds 80% in hand and face transplantation and is well documented, whereas reports about antibody‐mediated rejection and chronic rejection remain scarce. Immunosuppression protocols commonly used at US centers are derived from solid organ transplantation protocols. Novel approaches to minimize rejections in VCA may include improved HLA matching and considerations toward cytomegalovirus infection status. New graft preservation techniques may decrease immunogenicity prior to transplant. Novel monitoring methods such as valid biomarkers, ultrasound biomicroscopy, and sentinel flaps may enable earlier diagnosis of rejection. Cell‐based therapies are being explored to achieve immunosuppressive regimen minimization or even tolerance induction. The efficacy of local immunosuppression in clinical VCA remains controversial. In conclusion, although immunosuppressive strategies adapted from SOT have demonstrated good midterm results, focusing on the unique features of VCA grafts may enable additional, more specific treatment strategies in the future and improved long‐term graft outcomes.

A Rationale for Age-Adapted Immunosuppression in Organ Transplantation.

Abstract Demographic changes are associated with a steady increase of older patients with end-stage organ failure in need for transplantation. As a result, the majority of transplant recipients are currently older than 50 years, and organs from elderly donors are more frequently used. Nevertheless, the benefit of transplantation in older patients is well recognized, whereas the most frequent causes of death among older recipients are potentially linked to side effects of their immunosuppressants. Immunosenescence is a physiological part of aging linked to higher rates of diabetes, bacterial infections, and malignancies representing the major causes of death in older patients. These age-related changes impact older transplant candidates and may have significant implications for an age-adapted immunosuppression. For instance, immunosenescence is linked to lower rates of acute rejections in older recipients, whereas the engraftment of older organs has been associated with higher rejection rates. Moreover, new-onset diabetes mellitus after transplantation is more frequent in the elderly, potentially related to corticosteroids, calcineurin inhibitors, and mechanistic target of rapamycin inhibitors. This review presents current knowledge for an age-adapted immunosuppression based on both, experimental and clinical studies in and beyond transplantation. Recommendations of maintenance and induction therapy may help to improve graft function and to design future clinical trials in the elderly.

NAD+ protects against EAE by regulating CD4+ T-cell differentiation.

CD4+ T cells are involved in the development of autoimmunity, including multiple sclerosis (MS). Here we show that nicotinamide adenine dinucleotide (NAD+) blocks experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, by inducing immune homeostasis through CD4+IFNγ+IL-10+ T cells and reverses disease progression by restoring tissue integrity via remyelination and neuroregeneration. We show that NAD+ regulates CD4+ T-cell differentiation through tryptophan hydroxylase-1 (Tph1), independently of well-established transcription factors. In the presence of NAD+, the frequency of T-bet−/− CD4+IFNγ+ T cells was twofold higher than wild-type CD4+ T cells cultured in conventional T helper 1 polarizing conditions. Our findings unravel a new pathway orchestrating CD4+ T-cell differentiation and demonstrate that NAD+ may serve as a powerful therapeutic agent for the treatment of autoimmune and other diseases.

Obesity and its impact on transplantation and alloimmunity.

Obesity has become an increasing problem in healthcare worldwide with far-reaching consequences. More obese patients with irreversible end-stage organ failure undergo organ transplantation, and organs from obese donors are more frequently used. A growing body of evidence suggests more frequent postoperative complications and inferior patient and graft survival linked to obesity. More recently, adipose tissue has been linked to chronic inflammatory processes potentially impacting alloimmune responses and graft quality.