The high rate of antigenic drift in seasonal influenza viruses necessitates frequent changes in vaccine composition. Recent seasonal H3 vaccines do not protect against swine-origin H3N2 variant (H3N2v) strains that recently have caused severe human infections. Here, we report a human VH1-69 gene-encoded monoclonal antibody (mAb) designated H3v-47 that exhibits potent cross-reactive neutralization activity against human and swine H3N2 viruses that circulated since 1989. The crystal structure and electron microscopy reconstruction of H3v-47 Fab with the H3N2v hemagglutinin (HA) identify a unique epitope spanning the vestigial esterase and receptor-binding subdomains that is distinct from that of any known neutralizing antibody for influenza A H3 viruses. MAb H3v-47 functions largely by blocking viral egress from infected cells. Interestingly, H3v-47 also engages Fcγ receptor and mediates antibody dependent cellular cytotoxicity (ADCC). This newly identified conserved epitope can be used in design of novel immunogens for development of broadly protective H3 vaccines.

A platys and B canis vogeli infection, either singularly or together, was widespread in free roaming dogs associated with remote Aboriginal communities in the Northern Territory and north-western New South Wales. Moreover, both A platys and B canis vogeli infections were associated with a reduction in mean platelet numbers in dog populations, particularly in young dogs. The fact that 51% of dogs infected with A platys alone and 72% dogs coinfected were thrombocytopenic compared to 27% of uninfected dogs suggests that the organism alone or in combination with B canis vogeli has the potential to cause thrombocytopenia and perhaps contribute to a clinical bleeding disorder in infected dogs.

As a consequence of adult neurogenesis, the olfactory bulb (OB) receives a continuous influx of newborn neurons well into adulthood. However, their rates of generation and turnover, the factors controlling their survival, and how newborn neurons intercalate into adult circuits are largely unknown. To visualize the dynamics of adult neurogenesis, we produced a line of transgenic mice expressing GFP in Ϸ70% of juxtaglomerular neurons (JGNs), a population that undergoes adult neurogenesis. Using in vivo twophoton microscopy, time-lapse analysis of identified JGN cell bodies revealed a neuronal turnover rate of Ϸ3% of this population per month. Although new neurons appeared and older ones disappeared, the overall number of JGNs remained constant. This approach provides a dynamic view of the actual appearance and disappearance of newborn neurons in the vertebrate central nervous system, and provides an experimental substrate for functional analysis of adult neurogenesis.neurogenesis ͉ olfaction N ewborn neurons in the adult mammalian brain continuously migrate into the hippocampus and the olfactory bulb (OB) (1, 2). In the OB, newborn neurons originate in the subventricular zone and differentiate into two distinct populations of interneurons: granule cells and juxtaglomerular neurons (JGNs). Adult neurogenesis in the mammalian brain was discovered and has been primarily analyzed by methods that label dividing cells by incorporation of labeled cyclic nucleotides, such as radiolabeled thymidine or the uridine analogue 5-bromo-2-deoxyuridine (BrdUrd). These methods have significant limitations. For example, neither radiolabeled thymidine nor BrdUrd are neuron-specific, and both can be analyzed only in fixed tissue after histological processing. These caveats and others (see discussions in refs. 3 and 4) limit direct analysis of the dynamics of neurogenesis, such as turnover rates and subtle changes in levels of neurogenesis in response to different experimental conditions and manipulations.To study adult neurogenesis using an alternative approach, we developed transgenic mice expressing GFP in a subset of JGNs and imaged adult neurogenesis over periods of up to 3 months, in vivo. We observed an Ϸ3%-per-month turnover rate of JGN in the OB. The number of newly appearing JGNs (representing newborn neurons) was balanced by the number of JGNs disappearing (presumably by cell death) thereby maintaining a stable population of JGN neurons. ResultsLabeling of JGNs in Transgenic Mice. Using a methodology based on transgenic GFP expression under control of the Thy-1 promoter, Feng et al. (5) created a bevy of mouse lines in which distinct neuronal subpopulations were strongly labeled by GFP and other fluorescent proteins. These lines have proven invaluable for numerous in vivo imaging experiments (6-10) enabling visualization of axonal and dendritic dynamics in developing and adult animals. However, none of the existing lines of Thy-1-XFP mice has labeling in the regenerating populations of the OB (granule and juxtaglomerular neu...

H7N9 avian influenza virus causes severe infections and might have the potential to trigger a major pandemic. Molecular determinants of human humoral immune response to N9 neuraminidase (NA) proteins, which exhibit unusual features compared with seasonal influenza virus NA proteins, are ill-defined. We isolated 35 human monoclonal antibodies (mAbs) from two H7N9 survivors and two vaccinees. These mAbs react to NA in a subtype-specific manner and recognize diverse antigenic sites on the surface of N9 NA, including epitopes overlapping with, or distinct from, the enzyme active site. Despite recognizing multiple antigenic sites, the mAbs use a common mechanism of action by blocking egress of nascent virions from infected cells, thereby providing an antiviral prophylactic and therapeutic protection in vivo in mice. Studies of breadth, potency, and diversity of antigenic recognition from four subjects suggest that vaccination with inactivated adjuvanted vaccine induce NAreactive responses comparable to that of H7N9 natural infection.

To continue monitoring the prevalence and distribution of Ehrlichia chaffeensis (Rickettsiales: Rickettsiaeceae) in southern Indiana, a total of 498 Amblyomma americanum (L.) ticks (262 adults and 292 nymphs) was collected from five southern Indiana counties during May and June 1998. Ticks were pooled and examined for the presence of E. chaffeensis using nested polymerase chain reaction and primers specific for the 16S rRNA gene of E. chaffeensis. The average minimum infection rate for adult ticks collected in 1998 was 3.8% (ranging from 0 to 7.7% in various counties) as compared with previous average minimum infection rates of 1.6% in 1995 and 4.9% in 1997. None of the pools of A. americanum nymphs tested positive. In addition, blood samples were collected from 325 white-tailed deer taken in Indiana and 327 taken in Ohio in November 1998. Serum samples were tested for the presence of E. chaffeensis-like organisms reactive to antibodies using an indirect immunofluorescence assay (IFA). Antibodies were found in deer from six Indiana counties where infection rates ranged from 42.6 to 66.7% and in four Ohio countries where infection rates ranged from 4.4 to 25%. The results of this study reconfirm that E. chaffeensis is well established in southern Indiana and also provide the first evidence of E. chaffeensis-like organisms infecting white-tailed deer in Ohio, suggesting the need to survey Ohio ticks for the presence of Ehrlichia.

den faces of the HA head domain that interact with adjacent protomers. The TI-1 and TI-2 antigenic sites represent promising highly conserved, protective B cell epitopes that could be targets for inclusion in the rational design of broadly protective IAV vaccines. Methods Detailed methods are provided in the Supplemental Methods. Statistics. All statistics were processed using GraphPad Prism software, version 8 (GraphPad Software). For ELISAs, the mean optical density of 3 replicates was determined with SDs. For body weight measurements in mouse experiments, the mean initial body weight percentages were determined and the SEM calculated. Study approval. The mouse studies were conducted at the Association for Assessment and Accreditation of Laboratory Animal Careaccredited (AAALAC-accredited) laboratory animal research center of Vanderbilt University Medical Center with approval of the

SUMMARYBroadly reactive antibodies targeting the influenza A hemagglutinin (HA) head domain are thought to be rare and to require extensive somatic mutations or unusual structural features to achieve breadth against divergent HA subtypes. Here we describe common genetic and structural features of diverse human antibodies from several individuals recognizing the trimer interface (TI) of the influenza HA head, a recently identified site of vulnerability1–3. We examined the sequence of TI-reactive antibodies, determined crystal structures for TI antibody-antigen complexes, and analyzed the contact residues of the antibodies on HA to discover common genetic and structural features of TI antibodies. Our data reveal that many TI antibodies are encoded by a light chain variable gene segment incorporating a shared somatic mutation. In addition, these antibodies have a shared acidic residue in the heavy chain despite originating from diverse heavy chain variable gene segments. These studies show that the TI region of influenza HA is a major antigenic site with conserved structural features that are recognized by a common human B cell public clonotype. The canonical nature of this antibody-antigen interaction suggests that the TI epitope might serve as an important new target for structure-based vaccine design.

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