Cross-linking of CD54 on Burkitt Lymphoma Cell Line Raji and Ramos Induces FasL Expression by Reactive Oxygen Species and Apoptosis of Adjacent Cells in Fas/FasL Interaction

Bcells and their regulatory functions during Tuberculosis: Latency and active disease

Tuberculosis (TB) is a global epidemic with devastating consequences. Emerging evidence suggests that B-cells have the ability to modulate the immune response and understanding these roles during Mycobacterium tuberculosis (M.tb) infection can help to find new strategies to treat TB. The immune system of individuals with pulmonary TB form granulomas in the lung which controls the infection by inhibiting the M.tb growth and acts as a physical barrier. Thereafter, surviving M.tb become dormant and in most cases the host's immunity prevents TB reactivation. B-cells execute several immunological functions and are regarded as protective regulators of immune responses by antibody and cytokine production, as well as presenting antigen. Some of these B-cells, or regulatory B-cells, have been shown to express death-inducing ligands, such as Fas ligand (FasL). This expression and binding to the Fas receptor leads to apoptosis, a major immune regulation mechanism, in addition to the ability to induce T-cell tolerance. Here, I discuss the relevance of B-cells, in particular their non-humoral functions by addressing their regulatory properties during M.tb infection.

Neonatal hypoxic ischemic encephalopathy-related biomarkers in serum and cerebrospinal fluid

Neonatal hypoxic ischemic encephalopathy (HIE) is a common disease caused by perinatal asphyxia, a major cause of neonatal death, neurological behavior, and long-term disability. Currently, the diagnosis and prognosis of neonatal HIE are based on nervous system clinical manifestations, imaging and electrophysiological examination. These take time and late diagnosis allows brain injury to occur in newborns, so that infants of many brain injury missed the best treatment time, left with varying degrees of neurological sequelae. The use of biomarkers to monitor brain injury and evaluate neuroprotective effects might allow the early intervention and treatment of neonatal HIE to reduce mortality rates. This study reviewed the mechanism of neonatal hypoxic ischemic encephalopathy in relation to numerous brain-related biomarkers including NSE, S-100β, GFAP, UCH-L1, Tau protein, miRNA, LDH, and CK-BB. In early diagnosis of neonatal HIE, S-100β and activin A seems to be better biomarkers. Biomarkers with the greatest potential to predict long-term neurologic handicap of neonates with HIE are GFAP and UCH-L1 and when combined with other markers or brain imaging can increase the detection rate of HIE. Tau protein is a unique biological component of nervous tissues, and might have value for neonatal HIE diagnosis. Combination of more than two biological markers should be a future research direction.

Human B Cell-Derived Lymphoblastoid Cell Lines Constitutively Produce Fas Ligand and Secrete MHCII(+)FasL(+) Killer Exosomes

Immune suppression mediated by exosomes is an emerging concept with potentially immense utility for immunotherapy in a variety of inflammatory contexts, including allogeneic transplantation. Exosomes containing the apoptosis-inducing molecule Fas ligand (FasL) have demonstrated efficacy in inhibiting antigen-specific immune responses upon adoptive transfer in animal models. We report here that a very high frequency of human B cell-derived lymphoblastoid cell lines (LCL) constitutively produce MHCII⁺FasL⁺ exosomes that can induce apoptosis in CD4⁺ T cells. All LCL tested for this study (>20 independent cell lines) showed robust expression of FasL, but had no detectable FasL on the cell surface. Given this intracellular sequestration, we hypothesized that FasL in LCL was retained in the secretory lysosome and secreted via exosomes. Indeed, we found both MHCII and FasL proteins present in LCL-derived exosomes, and using a bead-based exosome capture assay demonstrated the presence of MHCII⁺FasL⁺ exosomes among those secreted by LCL. Using two independent experimental approaches, we demonstrated that LCL-derived exosomes were capable of inducing antigen-specific apoptosis in autologous CD4⁺ T cells. These results suggest that LCL-derived exosomes may present a realistic source of immunosuppressive exosomes that could reduce or eliminate T cell-mediated responses against donor-derived antigens in transplant recipients.

FasL-triggered death of Jurkat cells requires caspase 8-induced, ATP-dependent cross-talk between Fas and the purinergic receptor P2X(7)

Fas ligation via the ligand FasL activates the caspase-8/caspase-3-dependent extrinsic death pathway. In so-called type II cells, an additional mechanism involving tBid-mediated caspase-9 activation is required to efficiently trigger cell death. Other pathways linking FasL-Fas interaction to activation of the intrinsic cell death pathway remain unknown. However, ATP release and subsequent activation of purinergic P2X(7) receptors (P2X(7)Rs) favors cell death in some cells. Here, we evaluated the possibility that ATP release downstream of caspase-8 via pannexin1 hemichannels (Panx1 HCs) and subsequent activation of P2X(7)Rs participate in FasL-stimulated cell death. Indeed, upon FasL stimulation, ATP was released from Jurkat cells in a time- and caspase-8-dependent manner. Fas and Panx1 HCs colocalized and inhibition of the latter, but not connexin hemichannels, reduced FasL-induced ATP release. Extracellular apyrase, which hydrolyzes ATP, reduced FasL-induced death. Also, oxidized-ATP or Brilliant Blue G, two P2X(7)R blockers, reduced FasL-induced caspase-9 activation and cell death. These results represent the first evidence indicating that the two death receptors, Fas and P2X(7)R connect functionally via caspase-8 and Panx1 HC-mediated ATP release to promote caspase-9/caspase-3-dependent cell death in lymphoid cells. Thus, a hitherto unsuspected route was uncovered connecting the extrinsic to the intrinsic pathway to amplify death signals emanating from the Fas receptor in type II cells.

Killer B lymphocytes: the evidence and the potential

Immune regulation plays a critical role in controlling potentially dangerous inflammation and maintaining health. The Fas ligand/Fas receptor axis has been studied extensively as a mechanism of killing T cells and other cells during infections, autoimmunity, and cancer. FasL expression has been primarily attributed to activated T cells and NK cells. Evidence has emerged that B lymphocytes can express FasL and other death-inducing ligands, and can mediate cell death under many circumstances. Among B cell subsets, the expression of both Fas ligand and IL-10 is highest on the CD5(+) B cell population, suggesting that CD5(+) B cells may have a specialized regulatory function. The relevance of killer B cells to normal immune regulation, disease pathogenesis, and inflammation is discussed.