Comparing ultrastable lasers at 7 × 10-17 fractional frequency instability through a 2220 km optical fibre network

Ultrastable lasers are essential tools in optical frequency metrology enabling unprecedented measurement precision that impacts on fields such as atomic timekeeping, tests of fundamental physics, and geodesy. To characterise an ultrastable laser it needs to be compared with a laser of similar performance, but a suitable system may not be available locally. Here, we report a comparison of two geographically separated lasers, over the longest ever reported metrological optical fibre link network, measuring 2220 km in length, at a state-of-the-art fractional-frequency instability of 7 × 10-17 for averaging times between 30 s and 200 s. The measurements also allow the short-term instability of the complete optical fibre link network to be directly observed without using a loop-back fibre. Based on the characterisation of the noise in the lasers and optical fibre link network over different timescales, we investigate the potential for disseminating ultrastable light to improve the performance of remote optical clocks.

First industrial-grade coherent fiber link for optical frequency standard dissemination

We report on a fully bidirectional 680 km fiber link connecting two cities for which the equipment, the setup, and the characterization are managed for the first time by an industrial consortium. The link uses an active telecommunication fiber network with parallel data traffic and is equipped with three repeater laser stations and four remote double bidirectional erbium-doped fiber amplifiers. We report a short-term stability at 1 s integration time of 5.4×10^-16 in 0.5 Hz bandwidth and a long-term stability of 1.7×10^-20 at 65,000 s of integration time. The accuracy of the frequency transfer is evaluated as 3×10^-20. No shift is observed within the statistical uncertainty. We show a continuous operation over five days with an uptime of 99.93%. This performance is comparable with the state-of-the-art coherent links established by National Metrology Institutes in Europe. It is a first step in the construction of an optical fiber network for metrology in France, which will give access to an ultrahigh performance frequency standard to a wide community of scientific users.

Gender influences herpes simplex virus type 1 infection in normal and gamma interferon-mutant mice

Gender influences the incidence and severity of some bacterial and viral infections and autoimmune diseases in animal models and humans. To determine a gender-based difference, comparisons were made between male and female mice inoculated with herpes simplex virus type 1 (HSV-1) by the corneal route. Mortality was higher in the male mice of the three strains tested: 129/Sv//Ev wild type, gamma interferon (IFN-gamma) knockout (GKO), and IFN-gamma receptor knockout (RGKO). Similarly, in vivo HSV-1 reactivation occurred more commonly in male mice, but the male-female difference in reactivation was restricted to the two knockout strains and was not seen in the 129/Sv//Ev control. Comparison among male mice of the three strains showed a higher mortality of the RGKO mice and a higher reactivation rate of the GKO and RGKO mice than of the 129/Sv//Ev males. In contrast, female RGKO and GKO mice did not differ from female 129/Sv//Ev controls in either mortality or reactivation. HSV-1 periocular and eyelid disease was also more severe in male and dihydrotestosterone (DHT)-treated female mice than in control female mice. These results show a consistent gender difference in HSV-1 infection, with a worse outcome in male mice. In addition, the results comparing GKO and RGKO mice to controls show differences only in male mice, suggesting that some effects of IFN-gamma, a key immunoregulatory molecule, are gender specific.

Gamma interferon (IFN-gamma) receptor null-mutant mice are more susceptible to herpes simplex virus type 1 infection than IFN-gamma ligand null-mutant mice

Mouse strains with null mutations in the gamma interferon gene (Ifng) or the gamma interferon receptor gene (Ifngr) have been engineered. The use of these strains as animal models of viral and bacterial infections has enhanced our understanding of the role of gamma interferon (IFN-gamma) in the host immune response. However, direct comparisons between Ifng-/- (GKO) and Ifngr-/- (RGKO) mice have been problematic because previously available strains of these mice have had different genetic backgrounds (i.e., C57BL/6 and BALB/c for GKO mice and 129/Sv//Ev for RGKO mice). To enable direct comparison of herpes simplex virus type 1 (HSV-1) infections in GKO and RGKO mice, we introduced the IFN-gamma null mutation into the 129/Sv//Ev background. We report that, after HSV-1 inoculation, mortality was significantly greater in RGKO mice than in GKO mice (38 versus 23%, P = 0.0001). Similarly, the mortality from vaccinia virus challenge was significantly greater in RGKO mice than in GKO mice. With differences in genetic background excluded as a confounding issue, these results are consistent with the existence of an alternative ligand(s) for the IFN-gamma receptor that is also capable of mediating protection against viral challenge.

Role for gamma interferon in control of herpes simplex virus type 1 reactivation

Observation of chronic inflammatory cells and associated high-level gamma interferon (IFN-gamma) production in ganglia during herpes simplex type 1 (HSV-1) latent infection in mice (E. M. Cantin, D. R. Hinton, J. Chen, and H. Openshaw, J. Virol. 69:4898-4905, 1995) prompted studies to determine a role of IFN-gamma in maintaining latency. Mice lacking IFN-gamma (GKO mice) or the IFN-gamma receptor (RGKO mice) were inoculated with HSV-1, and the course of the infection was compared with that in IFN-gamma-competent mice with the same genetic background (129/Sv//Ev mice). A time course study showed no significant difference in trigeminal ganglionic viral titers or the timing of establishment of latency. Spontaneous reactivation resulting in infectious virus in the ganglion did not occur during latency in any of the mice. However, 24 h after the application of hyperthermic stress to mice, HSV-1 antigens were detected in multiple neurons in the null mutant mice but in only a single neuron in the 129/Sv//Ev control mice. Mononuclear inflammatory cells clustered tightly around these reactivating neurons, and by 48 h, immunostaining was present in satellite cells as well. The incidence of hyperthermia-induced reactivation as determined by recovery of infectious virus from ganglia was significantly higher in the null mutant than in control mice: 11% in 129/Sv//Ev controls, 50% in GKO mice (P = 0.0002), and 33% in RGKO mice (P = 0.03). We concluded that IFN-gamma is not involved in the induction of reactivation but rather contributes to rapid suppression of HSV once it is reactivated.

Detection of herpes simplex virus DNA sequences in human blood and bone marrow cells

Herpes simplex virus type 1 (HSV1) establishes latent infections in neural tissues of humans and experimental animals. Utilizing a sensitive polymerase chain reaction (PCR) assay we detected HSV DNA sequences in blood cells of healthy prospective bone marrow transplant (BMT) donors and patients. In three healthy individuals studied, HSV DNA sequences were found in all blood cell types and also in bone marrow cells as well as in stem cell progenitor colonies isolated from in vitro cultures. Studies of BMT donor-recipient pairs suggested that HSV reactivation may occur in hematopoietic cells after transplantation, as the PCR signal intensity increased over time simultaneous with an increased antibody titer to HSV. In a mouse model for HSV infection, HSV DNA sequences were found in blood and bone marrow cells at the latent stage of infection, after intravenous (IV) inoculation, but not after ocular inoculation. These studies suggest that bone marrow cells may be an additional site of HSV latency capable of reactivation after BMT. These studies have broad implications for understanding pathogenesis of HSV disease and are of particular significance in situations where allogeneic bone marrow cells are given therapeutically.

Persistence of herpes simplex virus DNA in rabbit corneal cells

Corneal cell cultures were established from the corneas of rabbits killed during a period of latency 118 d after ocular infection with the RE strain of herpes simplex virus (HSV). DNA was isolated from frozen cell pellets of 42 cell cultures that did not develop viral cytopathic effects during 44 d in culture. Using the polymerase chain reaction (PCR) to amplify HSV thymidine kinase (TK) gene sequences, HSV-specific DNA was detected in 15 of 42 culture-negative cell cultures. Subsequent reamplification, using nested primers that were complementary to HSV TK sequences internal to the orginal primers, resulted in eight additional culture-negative samples showing positive hybridization for HSV TK DNA. Twenty three of the 42 virus culture-negative corneal cell cultures tested by PCR were found to contain HSV genetic material. Detailed examination of the clinical histories of the eyes from which the corneal cultures were obtained showed no correlation between increased frequency or severity of epithelial disease, stromal disease, or virus shedding and more frequent isolation of virus or detection of HSV-specific DNA. These studies document that HSV DNA residues in the corneas of HSV-infected rabbits up to 118 d post-infection. About 10% of the eyes contained virus that could be reactivated in culture, whereas an additional 55% of the eyes contained DNA sequences homologous to a portion of the HSV TK gene.

Evaluation of antiviral immunity using vaccinia virus recombinants expressing cloned genes for herpes simplex virus type 1 glycoproteins

Immunization of mice with vaccinia virus recombinants expressing the glycoproteins B or D of herpes simplex virus type 1 (HSV-1) induced humoral antibody as well as multiple aspects of HSV-1-specific T lymphocyte-mediated responses. However, vaccinated mice were not completely resistant to HSV-1 challenge and were unable to eliminate an epithelial infection rapidly. Evidence is presented which indicates that immunization with either vaccinia virus recombinant, while inducing the necessary protective populations of CD4+ T lymphocytes, fails to induce the complementing CD8+ cytotoxic T lymphocytes necessary for high levels of protection against a primary HSV-1 infection. These findings are discussed with relevance to the future development of anti-HSV vaccines.

Cytotoxic T lymphocytes. Their relevance in herpesvirus infections

We have used recombinant vaccinia viruses expressing the cloned genes coding for glycoprotein B (gB) or glycoprotein D (gD) of HSV-1 to analyze the role of HSV-1--specific cytotoxic T lymphocytes (CTL) in antiviral immunity. Various studies in mice revealed that either vector could stimulate some aspects of HSV-1--specific immunity, but surprisingly, HSV-specific CTL were not induced. Even though gD appeared to be a target antigen for class II-MHC-restricted CTL, neither the gB or the gD vector was capable of forming a target-cell complex that was recognized by class I-MHC-restricted HSV-specific CTL. The inability of these major extracellular glycoproteins to act as CTL-target antigens was even more unusual in light of the ability of CTL to apparently recognize the immediate early genes of HSV, none of which are considered to be expressed on the surface of infected cells. The selective failure of either the gB or gD vector to induce numerous aspect of anti-HSV immunity in the absence of a CTL response allowed us to assess the consequence of this failure in terms of the level of protective immunity against HSV challenge seen in vector-immunized mice. These studies suggest that this failure to induce HSV-specific CTL appears to minimize the protective response to only efficiently protecting against low-challenge doses of HSV-1. These findings are discussed with relevance to the role of CTL in the control of herpesvirus infections.