Exposure to Secreted Bacterial Factors Promotes HIV-1 Replication in CD4+ T Cells

Microbial translocation is associated with systemic immune activation in HIV-1 disease. Circulating T cells can encounter microbial products in the bloodstream and lymph nodes, where viral replication takes place. The mechanisms by which bacteria contribute to HIV-associated pathogenesis are not completely deciphered. Here, we examined how bacteria may impact T cell function and viral replication. We established cocultures between a panel of live bacteria and uninfected or HIV-1-infected activated peripheral blood CD4-positive (CD4+) T cells. We show that some bacteria, such as Escherichia coli and Acinetobacter baumannii, sustain lymphocyte activation and enhance HIV-1 replication. Bacteria secrete soluble factors that upregulate CD25 and ICAM-1 cell surface levels and activate NF-κB nuclear translocation. Our data also demonstrate that CD25 polarizes at the virological synapse, suggesting a previously unappreciated role of CD25 during viral replication. These findings highlight how interactions between bacterial factors and T cells may promote T cell activation and HIV-1 replication. IMPORTANCE People living with HIV suffer from chronic immune activation despite effective antiretroviral therapy. Early after infection, HIV-1 actively replicates in the gut, causing the breakage of the intestinal epithelial barrier and microbial translocation. Microbial translocation and chronic immune activation have been proven linked; however, gaps in our knowledge on how bacteria contribute to the development of HIV-related diseases remain. Whether T cells in the peripheral blood react to bacterial products and how this affects viral replication are unknown. We show that some bacteria enriched in people living with HIV activate T cells and favor HIV-1's spread. Bacteria release soluble factors that cause the overexpression of cellular molecules related to their activation state. T cells overexpressing these molecules also replicate HIV-1 more efficiently. These results help us learn more about how HIV-1, T cells, and bacteria interact with each other, as well as the mechanisms behind chronic immune activation.

Type I interferon response and vascular alteration in chilblain-like lesions during the COVID-19 outbreak

Background

The outbreak of chilblain‐like lesions (CLL) during the COVID‐19 pandemic has been reported extensively, potentially related to SARS‐CoV‐2 infection, yet its underlying pathophysiology is unclear.

Objectives

To study skin and blood endothelial and immune system activation in CLL in comparison with healthy controls and seasonal chilblains (SC), defined as cold‐induced sporadic chilblains occurring during 2015 and 2019 with exclusion of chilblain lupus.

Methods

This observational study was conducted during 9–16 April 2020 at Saint‐Louis Hospital, Paris, France. All patients referred with CLL seen during this period of the COVID‐19 pandemic were included in this study. We excluded patients with a history of chilblains or chilblain lupus. Fifty patients were included.

Results

Histological patterns were similar and transcriptomic signatures overlapped in both the CLL and SC groups, with type I interferon polarization and a cytotoxic–natural killer gene signature. CLL were characterized by higher IgA tissue deposition and more significant transcriptomic activation of complement and angiogenesis factors compared with SC. We observed in CLL a systemic immune response associated with IgA antineutrophil cytoplasmic antibodies in 73% of patients, and elevated type I interferon blood signature in comparison with healthy controls. Finally, using blood biomarkers related to endothelial dysfunction and activation, and to angiogenesis or endothelial progenitor cell mobilization, we confirmed endothelial dysfunction in CLL.

Conclusions

Our findings support an activation loop in the skin in CLL associated with endothelial alteration and immune infiltration of cytotoxic and type I IFN‐polarized cells leading to clinical manifestations.

Activation endothéliale associée aux ANCA IgA au cours des lésions de lésions acrales pendant l’épidémie de COVID-19

Introduction

Matériel et méthodes

Résultats

Discussion

Salivary C-reactive protein among at-risk adolescents: A methods investigation of out of range immunoassay data

Inflammatory markers including C-Reactive Protein (CRP) are increasingly used within research and clinical settings. Yet, varying methodologies for cleaning immunoassay data with out of range (OOR) samples may alter characteristic levels of CRP, thereby obscuring interpretation and reliability. This study investigated the influence of eight immunoassay OOR data treatment techniques on salivary CRP (sCRP) samples from at-risk adolescents. Participants from the 'Sleep and Education: learning New Skills Early' (SENSE) Study were 86 adolescents at-risk for depression (50 female), aged 14.29 years (SD = 1.04). ANOVA results showed no statistically significant differences in average morning (F(7, 590) = 1.24, p = .28) and evening (F(7, 599)=1.29, p = .25) values produced by each OOR data cleaning technique. However, varying techniques produced differences in the magnitude of Pearson's correlations between consecutive saliva samples (r's between 0.27-0.78), and influenced the significance of a sCRP diurnal pattern; two techniques produced statistically higher morning than evening sCRP levels (t(85) = 2.70, p = .01 and t(85) = 2.67, p = .01), whereas six techniques failed to find statistical differences between morning and evening sCRP levels (p's >.05). Varying techniques also produced statistically divergent associations between sCRP and age and depressive symptoms. Results from this study provide evidence for the temporal stability of sCRP among adolescents, show winsorization as an effective OOR data management technique, and highlight the influence of methodological decisions in cleaning salivary biomarker data and the need for consistency within the field.

Near-concentric Fabry-Pérot cavity for continuous-wave laser control of electron waves

Manipulating free-space electron wave functions with laser fields can bring about new electron-optical elements for transmission electron microscopy (TEM). In particular, a Zernike phase plate would enable high-contrast TEM imaging of soft matter, leading to new opportunities in structural biology and materials science. A Zernike phase plate can be implemented using a tight, intense continuous laser focus that shifts the phase of the electron wave by the ponderomotive potential. Here, we use a near-concentric cavity to focus 7.5 kW of continuous-wave circulating laser power at 1064 nm into a 7 µm mode waist, achieving a record continuous laser intensity of 40 GW/cm². Such parameters are sufficient to impart a phase shift of 1 rad to a 10 keV electron beam, or 0.16 rad to a 300 keV beam. Our numerical simulations confirm that the standing-wave phase shift profile imprinted on the electron wave by the intra-cavity field can serve as a nearly ideal Zernike phase plate.

Cooperative Lamb shift in a mesoscopic atomic array

According to quantum electrodynamics, the exchange of virtual photons in a system of identical quantum emitters causes a shift of its energy levels. Such shifts, known as cooperative Lamb shifts, have been studied mostly in the near-field regime. However, the resonant electromagnetic interaction persists also at large distances, providing coherent coupling between distant atoms. Here, we report a direct spectroscopic observation of the cooperative Lamb shift of an optical electric-dipole transition in an array of Sr(+) ions suspended in a Paul trap at inter-ion separations much larger than the resonance wavelength. By controlling the precise positions of the ions, we studied the far-field resonant coupling in chains of up to eight ions, extending to a length of 40  μm. This method provides a novel tool for experimental exploration of cooperative emission phenomena in extended mesoscopic atomic arrays.

Vectorial phase retrieval for linear characterization of attosecond pulses

The waveforms of attosecond pulses produced by high-harmonic generation carry information on the electronic structure and dynamics in atomic and molecular systems. Current methods for the temporal characterization of such pulses have limited sensitivity and impose significant experimental complexity. We propose a new linear and all-optical method inspired by widely used multidimensional phase retrieval algorithms. Our new scheme is based on the spectral measurement of two attosecond sources and their interference. As an example, we focus on the case of spectral polarization measurements of attosecond pulses, relying on their most fundamental property-being well confined in time. We demonstrate this method numerically by reconstructing the temporal profiles of attosecond pulses generated from aligned CO(2) molecules.

Suicide attempt in first-episode psychosis: a 7.4 year follow-up study

BACKGROUND

Individuals with first-episode psychosis demonstrate high rates of suicide attempt (SA).

AIMS

1) To examine the prevalence of, and risk factors for, SA in a first-episode psychosis (FEP) cohort over a 7.4 year follow-up period. 2) To investigate differences between single versus multiple suicide attempters.

METHODS

This study reports baseline and follow-up data from a naturalistic, prospective follow-up of 413 FEP patients treated at a specialist early psychosis centre. Assessments were conducted at treatment entry, initial symptom remission or stabilization, and long term follow-up. Binary logistic regression models were used to assess unadjusted and adjusted associations between early illness and sociodemographic characteristics and two outcome measures: any SA during follow-up; and multiple SAs.

RESULTS

Follow-up data were available for 282 participants. Sixty-one (21.6%) made a suicide attempt over the follow-up period, including 12 successful suicides. The following baseline risk factors increased the risk of any SA: history of self-harm (OR=4.27; p<0.001), suicidal tendencies (OR=2.30; p=0.022), being depressed for >50% of the initial psychotic episode (OR=2.49; p=0.045), and hopelessness (OR=2.03; p=0.030). History of problem alcohol use increased the risk of multiple SAs (OR=4.43; 95% CI (1.05-18.7); p=0.043).

DISCUSSION

The prevalence of suicide attempt in this study exceeds reports from short-term FEP studies but is comparable to longer term follow-up studies, indicating that risk remains elevated for at least 7 years following commencement of treatment. The key predictor of future suicide attempt was previous self-harm, indicating that interventions for self-harm are required.

Detection and imaging of non-contractile inclusions and sarcomeric anomalies in skeletal muscle by second harmonic generation combined with two-photon excited fluorescence

The large size of the multinucleated muscle fibers of skeletal muscle makes their examination for structural and pathological defects a challenge. Sections and single fibers are accessible to antibodies and other markers but imaging of such samples does not provide a three-dimensional view of the muscle. Regrettably, bundles of fibers cannot be stained or imaged easily. Two-photon microscopy techniques overcome these obstacles. Second harmonic generation (SHG) by myosin filaments and two-photon excited fluorescence (2PEF) of mitochondrial and lysosomal components provides detailed structural information on unstained tissue. Furthermore, the infrared exciting light can penetrate several layers of muscle fibers and the minimal processing is particularly valuable for fragile biopsies. Here we demonstrate the usefulness of SHG, combined with 2PEF, to reveal enlarged lysosomes and accumulations of non-contractile material in muscles from the mouse model for the lysosomal storage disorder Pompe disease (PD), and in biopsies from adult and infant PD patients. SHG and 2PEF also detect sarcomeric defects that may presage the loss of myofibrils in atrophying muscle and signify loss of elasticity. The combination of SHG and 2PEF should be useful in the analysis and diagnosis of a wide range of skeletal muscle pathologies.

Prevalence and correlates of comorbidity 8 years after a first psychotic episode

OBJECTIVE

While rates and correlates of comorbidity have been investigated in the early course of psychosis, little is known about comorbidity in the medium-to-longer term or its relationship with outcome.

METHOD

A total of 182 first-episode psychosis (FEP) patients who met DSM-IV criteria for a current psychotic disorder 8 years after index presentation were grouped according to concurrent comorbidity [no concurrent axis I disorder; concurrent substance use disorder (SUD); other concurrent axis I disorder; concurrent SUD and other axis I disorder]. Outcomes were compared between groups controlling for relevant covariates.

RESULTS

As much as 39% met criteria for one or more concurrent axis 1 diagnoses. Comorbidity was associated with greater severity of general psychopathology, but not with measures of functioning, treatment or negative symptoms.

CONCLUSION

Specific combinations of comorbid disorders may influence patterns of psychotic symptomatology. Routine examination of axis I disorders is warranted in the ongoing management of psychosis.

Hyperbaric oxygen therapy as a treatment for stage-I avascular necrosis of the femoral head

Avascular necrosis (AVN) of the head of the femur is a potentially crippling disease which mainly affects young adults. Although treatment by exposure to hyperbaric oxygen (HBO) is reported as being beneficial, there has been no study of its use in treated compared with untreated patients. We selected 12 patients who suffered from Steinberg stage-I AVN of the head of the femur (four bilateral) whose lesions were 4 mm or more thick and/or 12.5 mm or more long on MRI. Daily HBO therapy was given for 100 days to each patient. All smaller stage-I lesions and more advanced stages of AVN were excluded. These size criteria were chosen in order to compare outcomes with an identical size of lesion in an untreated group described earlier. Overall, 81% of patients who received HBO therapy showed a return to normal on MRI as compared with 17% in the untreated group. We therefore conclude that hyperbaric oxygen is effective in the treatment of stage-I AVN of the head of the femur.

Commonsense design of patella implant: four years of clinical experience with 124 patients

BACKGROUND

Patella resurfacing in Total knee Arthroplasty still is an issue of controversy, that results from the statistically poor performance of patella implants. Since the basic fault of conventional designs, in our opinion, is the inadequate thickness of the polyethylene, an innovative patella was designed and rules of technique were set to optimize the surgical procedure.

METHODS

Since July 1998 we have employed the new patella in 124 consecutive patients undergoing total knee arthroplasty. They had the patella routinely resurfaced with an implant of a special design of a concave undersurface and a convex (dome) articulating surface. The thickness of the entire implant was uniform at all areas of contact. The bony patella was prepared with a concave reamer and shaped into a dome with a shallow central hole. Fixation with cement gave an optimally stable implant to shear forces and resistance to wear.

RESULTS

All patients were studied prospectively and followed up to five years. Results were related specifically to performance of the patella as a part of the entire joint. Two patients died from unrelated causes. Four patients had delayed wound healing. One sustained a transverse fracture of the patella already healed with minimal displacement when she came to our attention. One sustained avulsion of the patella tendon from the tuberosity, which underwent surgical reattachment. Rest pain score (10-0) improved from 5.2 to 0.5. Activity pain score (10-0) improved from 9.0 to 1.4. Walking score (0-10) improved from 3.2 to 8.2. Stairs negotiation (0-10) improved from 2.8 to 8.0 and ADL Function (0-10) improved from 4.3 to 8.2.

CONCLUSION

The special technique of resurfacing of the patella was developed during a short learning period. The new design of the patella implant, eight mm thick at any point of contact gave excellent and good results in 91%. There were no intra operative complications. During five years of follow up two complication were encountered and treated successfully: a minimally displaced transverse fracture and an avulsion of the patella tendon from the tuberosity. None of the patellae components required replacement. In our opinion the new design of bio-mechanically reliable patella implant will regain confidence of surgeons who presently refrain from patella resurfacing.

Wear pattern of retrieved patellar implants

The so-called "papillon" pattern of polyethylene wear of 17 patellar components from 5 Kinematic and 12 Total Condylar prostheses, retrieved after an average of 80 months in situ, was studied. The primary diagnosis was osteoarthritis in all cases. Four modes of damage were observed: polishing in 13 cases, delamination in 12, cold flow in 6 and scratching in 3. The median total area of polyethylene damage was 76.5% for polishing, 70.6% for delamination, 35.3% for cold flow and 17.6% for scratching. The importance of the conformity of the Kinematic patellar component in order to decrease contact stresses was confirmed. The average contact stresses on the nonconforming total Condylar patellar component (12.9 kgf/mm2), were significantly higher (p < 0.002) than the average contact stresses on the conforming Kinematic patellar component (2.9 kgf/mm2). The area of wear was smaller for the nonconforming Total Condylar (357.2 mm2) than for the conforming Kinematic patella (439.2 mm2). This difference, however, is not statistically significant. The average weight of the patients with a Kinematic Knee (74.5 kg) was higher than that of patients with a Total Condylar knee (66 kg), but the difference was not significant. The high incidence of significant wear of the patellar components indicates that a basic deficiency is present in the design of patellar implants, and calls for the improvement of two mechanical features: adequate thickness of the polyethylene implant and conforming articulating surfaces.

A comparative biomechanical study of the strength of the bony patella following dome cut or uniplanar cut in total knee arthroplasty

This study was designed to investigate whether there is a difference in the strength of the bony patella following preparation either with a dome configuration or with a regular uniplanar cut in total knee arthroplasty. For each test 4 cadaveric patellae were used. Two of the 4 patellae were prepared with a regular uniplanar cut and 2 were prepared into a dome shape with a circumferential wall, using a concave reamer. The thickness of each patella after preparation was [figure 1 & 2: see text] 15 mm. The tests were performed using an impact drop weight apparatus. In the first two tests, which tested the resistance of the patella to tensile force and evaluated the strength of the patella by impact load while under tension, the soft tissues were torn, with no harm to the bony patella. In the third test, which evaluated the resistance of the patella without tension against impact load, the force required to fracture the dome-shaped patella was greater than for the traditional uniplanar cut (500 Kg vs 350 Kg). Dome shape with circumferential wall preparations of the bony patella in total knee arthroplasty were stronger in resisting external impact than the conventional uniplanar cut patella. This established the rationale for our use of the dome-shaped patella implant with a concave undersurface.

Allo- and autotransplantation of mature teeth in monkeys: a sequential time-related histoquantitative study of periodontal and pulpal healing

Root resorption is known to be the most relevant complication determining the long-term prognosis of allotransplanted teeth, and it is initiated during the first few postoperative months. The aim of the present study was to quantitatively assess the dynamics of the periodontal ligament (PDL) and pulpal healing reactions during the first 8 weeks after allotransplantation of mature teeth. The material comprised 112 maxillary central and mandibular lateral incisors of 28 mature green Vervet monkeys, immunogenetically untested, and only matched according to the size of the grafts. Donors and recipients exchanged simultaneously both maxillary incisors and one mandibular incisor, whereas the contralateral mandibular incisors were autotransplanted as controls. At random, every second maxillary allograft was endodontically treated preoperatively. Histoquantitative analysis of the PDL and pulpal healing reactions was carried out after 1, 2, 4 and 8 weeks on serial cross-sections of the grafts in 6, 6, 6 and 8 monkeys, respectively. Necrosis zones in the PDL were prominent in both auto- and allografts after 1 week. Inflammation in the PDL dominated healing in all types of grafts 1 week after transplantation, whereas it subsided significantly after 2 weeks in autografts compared to allografts (P = 0.005). Inflammatory resorption (IR) became prominent after 4 weeks in autografts and this remained stationary. In contrast, IR initiated significantly earlier in allografts compared to autografts after 2 weeks (P = 0.007), and this type of resorption was further increasing in allografts after 4 and 8 weeks. Endodontic treatment, however, reduced IR nearly totally in the allografts with time. Replacement resorption (RR) was nearly absent in autografts. In contrast, allografts showed increasing appearance of RR with time, initiating at 4 weeks. By removing IR from the allografts by endodontic treatment, RR was unmasked significantly at 4 weeks (P = 0.02) and dominated most of the periodontal ligament (70%) after 8 weeks (P = 0.0004). Within the 8 postoperative weeks autografts showed healing with increasing amount of normal PDL reaching significantly higher levels compared to allografts already after 2 weeks (P = 0.02), with increasing differences thereafter. In most allografts, the normal PDL occupied less than 10% of the entire root surface and was located in the supra-alveolar cervical region. Downgrowth of periodontal pocket epithelium was absent or found very infrequently in all groups irrespective of type, time and treatment. In conclusion, the healing of allo- and autotransplanted mature teeth differed significantly on several aspects during the first 8 postoperative weeks. The recorded differences included a higher amount of inflammation in the PDL of allografts after 2 weeks, inflammatory resorption from the second week, and replacement resorption dominating in the eighth week, indicated that an immunologic stimulus for root resorption existed in the allogenic PDL apart from the pulp. Furthermore, specific healing reactions was found in the cervical region with almost identical gingival healing in auto- and allografts.

Effects of temperature, storage time and media on periodontal and pulpal healing after replantation of incisors in monkeys

The effect of temperature of various storage media and at varying storage periods upon periodontal ligament (PDL) and pulpal healing after tooth replantation was examined in green vervet monkeys (Cercopithecus aethiops). Mandibular lateral incisors with mature root formation were extracted and kept in dry storage at 22, 4 and -18 degrees C; in saline at 37, 22, 4 and -18 degrees C; or in saliva (i.e. in the buccal vestibule) at 37 degrees C for either 60 or 120 min prior to replantation. The animals were sacrificed 8 weeks after replantation and the replanted teeth examined histometrically. The following histological parameters were registered for each tooth: normal PDL, surface resorption, inflammatory resorption, replacement resorption (ankylosis), downgrowth of pocket epithelium, periapical inflammatory changes, and the extent of vital pulp. A total of 125 replanted teeth were examined. Storage in saliva at 37 degrees C showed a similar amount of normal PDL compared to saline storage for both 60 and 120 min. Saline storage for 60 or 120 min showed no difference in the extent of normal PDL when storage was compared at 37, 22 and 4 degrees C. However, storage at -18 degrees C resulted in significantly less normal PDL than storage at other temperatures. Dry storage for 60 min showed significantly less root resorption at 4 degrees C compared to 22 degrees C. Furthermore, dry storage at -18 degrees C showed significantly less normal PDL than storage at 4 degrees C. When the dry storage period was extended to 120 min, no difference was found between 22, 4 and -18 degrees C. It is concluded that the temperature (above 0 degrees C) of the storage medium is of importance only for dry storage and in such a situation only for shorter extra-alveolar periods, i.e. for 60-min storage and not for 120 min, where extensive destruction of the PDL always takes place. It is suggested that the temperature effect of 4 degrees C could be related to less evaporation from the PDL and thereby less damage to the PDL cells or a strict temperature effect upon cell metabolism. Pulp healing in all the cases was limited to the entrance of the pulp canal, and no significant pattern was found between storage media, time and temperature.

Enhanced presentation of major histocompatibility complex class I-restricted human immunodeficiency virus type 1 (HIV-1) Gag-specific epitopes after DNA immunization with vectors coding for vesicular stomatitis virus glycoprotein-pseudotyped HIV-1 Gag particles

In vivo priming of cytotoxic T lymphocytes (CTL) by DNA injection predominantly occurs by antigen transfer from DNA-transfected cells to antigen-presenting cells. A rational strategy for increasing DNA vaccine potency would be to use a delivery system that facilitates antigen uptake by antigen-presenting cells. Exogenous antigen presentation through the major histocompatibility complex (MHC) class I-restricted pathway of some viral antigens is increased after adequate virus-receptor interaction and the fusion of viral and cellular membranes. We used DNA-based immunization with plasmids coding for human immunodeficiency virus type 1 (HIV-1) Gag particles pseudotyped with vesicular stomatitis virus glycoprotein (VSV-G) to generate Gag-specific CTL responses. The presence of the VSV-G-encoding plasmid not only increased the number of mice displaying anti-Gag-specific cytotoxic response but also increased the efficiency of specific lysis. In vitro analysis of processing confirmed that exogenous presentation of Gag epitopes occurred much more efficiently when Gag particles were pseudotyped with the VSV-G envelope. We show that the VSV-G-pseudotyped Gag particles not only entered the MHC class II processing pathway but also entered the MHC class I processing pathway. In contrast, naked Gag particles entered the MHC class II processing pathway only. Thus, the combined use of DNA-based immunization and nonreplicating pseudotyped virus to deliver HIV-1 antigen to the immune system in vivo could be considered in HIV-1 vaccine design.

Effect of treatment delay upon pulp and periodontal healing of traumatic dental injuries -- a review article

Based on an analysis of the literature concerning parameters influencing the prognosis of traumatic dental injuries, few studies were found to have examined possible relationships between treatment delay and pulpal and periodontal ligament healing complications. It has been commonly accepted that all injuries should be treated on an emergency basis, for the comfort of the patient and also to reduce wound healing complications. For practical and especially economic reasons, various approaches can be selected to fulfill such a demand, such as acute treatment (i.e. within a few hours), subacute (i.e. within the first 24 h), and delayed (i.e. after the first 24 h). In this survey the consequences of treatment delay on pulpal and periodontal healing have been analyzed for the various dental trauma groups. Applying such a treatment approach to the various types of injuries, the following treatment guidelines can be recommended, based on our present rather limited knowledge of the effect of treatment delay upon wound healing. Crown and crown/root fractures: Subacute or delayed approach. Root fractures: Acute or subacute approach. Alveolar fractures: Acute approach (evidence however questionable). Concussion and subluxation: Subacute approach. Extrusion and lateral luxation: Acute or subacute approach (evidence however questionable). Intrusion: Subacute approach (evidence however questionable). Avulsion: If the tooth is not replanted at the time of injury, acute approach; otherwise subacute. Primary tooth injury: Subacute approach, unless the primary tooth is displaced into the follicle of the permanent tooth or occlusal problems are present; in the latter instances, an acute approach should be chosen. These treatment guidelines are based on very limited evidence from the literature and should be revised as soon as more evidence about the effect of treatment delay becomes available.

Human immunodeficiency virus type 1 entry into macrophages mediated by macropinocytosis

Whereas human immunodeficiency virus (HIV) infects various cell types by fusion at the plasma membrane, we observed a different entry route in human primary macrophages, in which macropinocytosis is active. Shortly after exposure of macrophages to HIV-1 and irrespective of viral envelope-receptor interactions, particles were visible in intracellular vesicles, which were identified as macropinosomes. Most virions appeared subsequently degraded. However, fusion leading to capsid release in the cytosol and productive infection could take place inside vesicles when particles were properly enveloped. These observations provide new insights into HIV-1 interactions with a cell target relevant to pathogenesis. They may have implications for the design of soluble inhibitors aimed at interfering with the fusion or entry processes.

HIV-1 Nef impairs MHC class II antigen presentation and surface expression

HIV-1-infected cells can avoid cytotoxic T lymphocyte killing by Nef-mediated down-regulation of surface MHC I. Here, we show that HIV-1 Nef inhibits MHC II restricted peptide presentation to specific T cells and thus may affect the induction of antiviral immune responses. Nef mediates this effect by reducing the surface level of mature (i.e., peptide-loaded) MHC II while increasing levels of immature MHC II, which are functionally incompetent because of their association with the invariant chain. Nef was the only HIV-1 gene product to possess this capacity, which was also observed in the context of the whole HIV-1 genome. Other proteins of the endocytic pathway were not affected by Nef expression, suggesting that Nef effects on MHC II did not result from a general alteration of the endocytic pathway. Response patterns to previously characterized mutations of Nef differed for Nef-induced modulation of mature and immature MHC II. Furthermore, the doses of Nef required to observe each of the two effects were clearly different, suggesting that Nef could affect MHC II peptide presentation through distinct mechanisms. Cooperation between those mechanisms may enable Nef to efficiently inhibit MHC II function.

Complications of K-wire fixation of fractures and dislocations in the hand and wrist

Kirschner wire (K-wire) fixation of fractures and dislocations of the hand and wrist is a common procedure. Of the 590 K-wire fixations performed on 236 patients, 36 (15.2%) experienced complications which included osteomyelitis, tendon rupture, nerve lesion, pin tract infection, pin loosening or migration. There were no deep soft-tissue pin infections or pyarthrosis. Technical failure, mainly when the procedure was performed by residents, and poor patient compliance were the major causes of complications. K-wire fixation is a simple but demanding procedure that cannot be left to an inexperienced resident. Elimination of technical failure, supervision in the operating room, close monitoring, prompt treatment upon discovery of a complication, and improvement of patient compliance can reduce the rate of complications.

Production and neurotropism of lentivirus vectors pseudotyped with lyssavirus envelope glycoproteins

We investigated the production efficiency and the gene transfer capacity in the central nervous system of HIV-1-based vectors pseudotyped with either the G protein of the Mokola lyssaviruses (MK-G), a neurotropic virus causing rabies disease, or the vesiculo-stomatitis G protein (VSV-G). Both envelopes induced syncitia in cell cultures. They were incorporated into vector particles and mature virions were observed by electron microscopy. Vector production was two- to sixfold more efficient with VSV-G than with MK-G. For equivalent amounts of physical particles, vector titration was 5- to 25-fold higher with VSV-G than with MK-G pseudotypes on cultured cells, and in vivo gene expression in mouse brain was more intense. Thus, VSV-G pseudotypes were produced more efficiently and were more infectious than MK-G pseudotypes. Tropism for brain cells was analyzed by intrastriatal injections in rats. Both pseudotypes preferentially transduced neurons (70-90% of transduced cells). Retrograde axonal transport was investigated by instilling vector suspensions in the rat nasal cavity. Both pseudotypes were efficiently transported to olfactive neuron bodies. Thus, although coating HIV-1 particles with rabdhovirus envelope glycoproteins enables them to enter neuronal cells efficiently, pseudotyping is not sufficient to confer the powerful neurotropism of lyssaviruses to lentivirus vectors.

Natural signal statistics and sensory gain control

We describe a form of nonlinear decomposition that is well-suited for efficient encoding of natural signals. Signals are initially decomposed using a bank of linear filters. Each filter response is then rectified and divided by a weighted sum of rectified responses of neighboring filters. We show that this decomposition, with parameters optimized for the statistics of a generic ensemble of natural images or sounds, provides a good characterization of the nonlinear response properties of typical neurons in primary visual cortex or auditory nerve, respectively. These results suggest that nonlinear response properties of sensory neurons are not an accident of biological implementation, but have an important functional role.

Nef is required for efficient HIV-1 replication in cocultures of dendritic cells and lymphocytes

Dendritic cells (DCs) are thought to play a crucial role in the pathogenesis of HIV-1 infection. DCs are believed to transport virus particles to lymph nodes before transfer to CD4(+) lymphocytes. We have investigated the role of Nef in these processes. HIV-1 replication was examined in human immature DC-lymphocyte cocultures and in DCs or lymphocytes separately. Using various R5-tropic and X4-tropic HIV-1 strains and their nef-deleted (Deltanef) counterparts, we show that Nef is required for optimal viral replication in immature DC-T cells clusters and in T lymphocytes. Nef exerts only a marginal role on viral replication in immature DCs alone as well as on virion capture by DCs, long-term intracellular accumulation and transmission of X4 strains to lymphocytes. We also show that wild-type and Deltanef virions are similarly processed for MHC-I restricted exogenous presentation by DCs. Taken together, these results help explain how HIV-1 Nef may affect viral spread and immune responses in the infected host.