Persistent Spin Dynamics in the S=1/2S=1/2 V15_{15} Molecular Nano-Magnet

We present muon spin lattice relaxation measurements in the V15 spin 1/2 molecular nano-magnet. We find that the relaxation rate in low magnetic fields (<5 kG) is temperature independent below ~10 K, implying that the molecular spin is dynamically fluctuating down to 12 mK. These measurements show that the fluctuation time increases as the temperature is decreased and saturates at a value of ~6 nsec at low temperatures. The fluctuations are attributed to V15 molecular spin dynamics perpendicular to the applied magnetic field direction, induced by coupling between the molecular spin and nuclear spin bath in the system.Comment: Accepted for publication in Phys. Rev. B, 5 pages, 5 figur

Vector Transmission of Leishmania Abrogates Vaccine-Induced Protective Immunity

Numerous experimental vaccines have been developed to protect against the cutaneous and visceral forms of leishmaniasis caused by infection with the obligate intracellular protozoan Leishmania, but a human vaccine still does not exist. Remarkably, the efficacy of anti-Leishmania vaccines has never been fully evaluated under experimental conditions following natural vector transmission by infected sand fly bite. The only immunization strategy known to protect humans against natural exposure is “leishmanization,” in which viable L. major parasites are intentionally inoculated into a selected site in the skin. We employed mice with healed L. major infections to mimic leishmanization, and found tissue-seeking, cytokine-producing CD4+ T cells specific for Leishmania at the site of challenge by infected sand fly bite within 24 hours, and these mice were highly resistant to sand fly transmitted infection. In contrast, mice vaccinated with a killed vaccine comprised of autoclaved L. major antigen (ALM)+CpG oligodeoxynucleotides that protected against needle inoculation of parasites, showed delayed expression of protective immunity and failed to protect against infected sand fly challenge. Two-photon intra-vital microscopy and flow cytometric analysis revealed that sand fly, but not needle challenge, resulted in the maintenance of a localized neutrophilic response at the inoculation site, and removal of neutrophils following vector transmission led to increased parasite-specific immune responses and promoted the efficacy of the killed vaccine. These observations identify the critical immunological factors influencing vaccine efficacy following natural transmission of Leishmania

2013 WSES guidelines for management of intra-abdominal infections

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