Development and Validation of a New Mouse Model to Investigate the Role of SV2A in Epilepsy.

SV2A is a glycoprotein present in the membranes of most synaptic vesicles. Although it has been highly conserved throughout evolution, its physiological role remains largely unknown. Nevertheless, Levetiracetam, a very effective anti-epileptic drug, has been recently demonstrated to bind to SV2A. At present, our understanding of the normal function of SV2A and its possible involvement in diseases like epilepsy is limited. With this study, we sought to develop a relevant model enabling analysis of SV2A's role in the occurrence or progression of epilepsy. For this purpose, we generated a floxed SV2A mouse model with conditional alleles carrying LoxP sites around exon 3 by means of a gene-targeting strategy. The SV2A lox/lox mouse line is indistinguishable from wild-type mice. When the recombination was observed in all cells, a model of mice with both SV2A alleles floxed around exon 3 recapitulated the phenotype of SV2A KO mice, including seizures. However, the specific invalidation of SV2A in the CA3 hippocampal region was not followed by epileptic seizures or decrease in the epileptic threshold on pentylenetetrazol (PTZ) test. These results demonstrate that the floxed SV2A mouse line has been successfully established. This transgenic mouse model will be useful for investigating SV2A functions related to cell types and developmental stages.

Impact of Pre-Transplant Anti-T Cell Globulin (ATG) on Immune Recovery after Myeloablative Allogeneic Peripheral Blood Stem Cell Transplantation.

BACKGROUND: Pre-transplant infusion of rabbit anti-T cell globulin (ATG) is increasingly used as prevention of graft-versus-host disease (GVHD) after allogeneic peripheral blood stem cell transplantation (PBSCT). However, the precise impact of pre-transplant ATG on immune recovery after PBSCT is still poorly documented. METHODS: In the current study, we compared immune recovery after myeloablative PBSCT in 65 patients who either received (n = 37) or did not (n = 28) pre-transplant ATG-Fresenius (ATG-F). Detailed phenotypes of circulating T, B, natural killer (NK) and invariant NKT (iNKT) cells were analyzed by multicolor flow cytometry at serial time-points from day 40 to day 365 after transplantation. Thymic function was also assessed by sjTREC quantification. Serious infectious events were collected up to 2 years post-transplantation. RESULTS: Pre-transplant ATG-F had a prolonged (for at least up to 1-year) and selective negative impact on the T-cell pool, while it did not impair the recovery of B, NK nor iNKT cells. Among T cells, ATG-F selectively compromised the recovery of naïve CD4+, central memory CD4+ and naïve CD8+ cells, while it spared effector memory T and regulatory T cells. Levels of sjTRECs were similar in both cohorts at 1-year after PBSCT, suggesting that ATG-F unlikely impaired thymopoiesis at long-term after PBSCT. Finally, the incidence and rate of serious infections were similar in both groups, while ATG-F patients had a lower incidence of grade II-IV acute graft-versus-host disease. CONCLUSIONS: Pre-transplant ATG-F induces long-lasting modulation of the circulating T-cell pool after myeloablative PBSCT, that may participate in preventing graft-versus-host disease without deeply compromising anti-pathogen defenses.

Neutrophil extracellular traps entrap and kill Borrelia burgdorferi sensu stricto spirochetes and are not affected by Ixodes ricinus tick saliva.

Lyme disease is caused by spirochetes of the Borrelia burgdorferi sensu lato complex. They are transmitted mainly by Ixodes ricinus ticks. After a few hours of infestation, neutrophils massively infiltrate the bite site. They can kill Borrelia via phagocytosis, oxidative burst, and hydrolytic enzymes. However, factors in tick saliva promote propagation of the bacteria in the host even in the presence of a large number of neutrophils. The neutrophil extracellular trap (NET) consists in the extrusion of the neutrophil's own DNA, forming traps that can retain and kill bacteria. The production of reactive oxygen species is apparently associated with the onset of NETs (NETosis). In this article, we describe NET formation at the tick bite site in vivo in mice. We show that Borrelia burgdorferi sensu stricto spirochetes become trapped and killed by NETs in humans and that the bacteria do not seem to release significant nucleases to evade this process. Saliva from I. ricinus did not affect NET formation by human neutrophils or its stability. However, it greatly decreased neutrophil reactive oxygen species production, suggesting that a strong decrease of hydrogen peroxide does not affect NET formation. Finally, round bodies trapped in NETs were observed, some of them staining as live bacteria. This observation could help contribute to a better understanding of the early steps of Borrelia invasion and erythema migrans formation after tick bite.

Ir-LBP, an ixodes ricinus tick salivary LTB4-binding lipocalin, interferes with host neutrophil function.

BACKGROUND: During their blood meal, ticks secrete a wide variety of proteins that can interfere with their host's defense mechanisms. Among these proteins, lipocalins play a major role in the modulation of the inflammatory response. METHODOLOGY/PRINCIPAL FINDINGS: We previously identified 14 new lipocalin genes in the tick Ixodes ricinus. One of them codes for a protein that specifically binds leukotriene B4 with a very high affinity (Kd: +/-1 nM), similar to that of the neutrophil transmembrane receptor BLT1. By in silico approaches, we modeled the 3D structure of the protein and the binding of LTB4 into the ligand pocket. This protein, called Ir-LBP, inhibits neutrophil chemotaxis in vitro and delays LTB4-induced apoptosis. Ir-LBP also inhibits the host inflammatory response in vivo by decreasing the number and activation of neutrophils located at the tick bite site. Thus, Ir-LBP participates in the tick's ability to interfere with proper neutrophil function in inflammation. CONCLUSIONS/SIGNIFICANCE: These elements suggest that Ir-LBP is a "scavenger" of LTB4, which, in combination with other factors, such as histamine-binding proteins or proteins inhibiting the classical or alternative complement pathways, permits the tick to properly manage its blood meal. Moreover, with regard to its properties, Ir-LBP could possibly be used as a therapeutic tool for illnesses associated with an increased LTB4 production.