Single cell transcriptomics shows that malaria promotes unique regulatory responses across multiple immune cell subsets

Plasmodium falciparum malaria drives immunoregulatory responses across multiple cell subsets, which protects from immunopathogenesis, but also hampers the development of effective anti-parasitic immunity. Understanding malaria induced tolerogenic responses in specific cell subsets may inform development of strategies to boost protective immunity during drug treatment and vaccination. Here, we analyse the immune landscape with single cell RNA sequencing during P. falciparum malaria. We identify cell type specific responses in sub-clustered major immune cell types. Malaria is associated with an increase in immunosuppressive monocytes, alongside NK and γδ T cells which up-regulate tolerogenic markers. IL-10-producing Tr1 CD4 T cells and IL-10-producing regulatory B cells are also induced. Type I interferon responses are identified across all cell types, suggesting Type I interferon signalling may be linked to induction of immunoregulatory networks during malaria. These findings provide insights into cell-specific and shared immunoregulatory changes during malaria and provide a data resource for further analysis.

STING activation promotes autologous type I interferon-dependent development of type 1 regulatory T cells during malaria

The development of highly effective malaria vaccines and improvement of drug-treatment protocols to boost antiparasitic immunity are critical for malaria elimination. However, the rapid establishment of parasite-specific immune regulatory networks following exposure to malaria parasites hampers these efforts. Here, we identified stimulator of interferon genes (STING) as a critical mediator of type I interferon production by CD4+ T cells during blood-stage Plasmodium falciparum infection. The activation of STING in CD4+ T cells by cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) stimulated IFNB gene transcription, which promoted development of IL-10- and IFN-γ-coproducing CD4+ T (type I regulatory [Tr1]) cells. The critical role for type I IFN signaling for Tr1 cell development was confirmed in vivo using a preclinical malaria model. CD4+ T cell sensitivity to STING phosphorylation was increased in healthy volunteers following P. falciparum infection, particularly in Tr1 cells. These findings identified STING expressed by CD4+ T cells as an important mediator of type I IFN production and Tr1 cell development and activation during malaria.

A case report of tracheal tenting to the skin: An option to tracheostomy for post-thyroidectomy tracheomalacia

Operating on a huge and long-standing goiter is challenging to the surgeon and anesthetist because of the possibility of tracheomalacia and collapse of the tracheal rings after extubation. We report our innovation of tenting the trachea to the skin using sutures (passed through the strap and sternocleidomastoid muscles) to prevent post-thyroidectomy tracheomalacia.

Plasmodium falciparum formins are essential for invasion and sexual stage development

The malaria parasite uses actin-based mechanisms throughout its lifecycle to control a range of biological processes including intracellular trafficking, gene regulation, parasite motility and invasion. In this work we assign functions to the Plasmodium falciparum formins 1 and 2 (FRM1 and FRM2) proteins in asexual and sexual blood stage development. We show that FRM1 is essential for merozoite invasion and FRM2 is required for efficient cell division. We also observed divergent functions for FRM1 and FRM2 in gametocyte development. Conditional deletion of FRM1 leads to a delay in gametocyte stage progression. We show that FRM2 controls the actin and microtubule cytoskeletons in developing gametocytes, with premature removal of the protein resulting in a loss of transmissible stage V gametocytes. Lastly, we show that targeting formin proteins with the small molecule inhibitor of formin homology domain 2 (SMIFH2) leads to a multistage block in asexual and sexual stage parasite development.

Malaria-driven expansion of adaptive-like functional CD56-negative NK cells correlates with clinical immunity to malaria

Natural killer (NK) cells likely play an important role in immunity to malaria, but the effect of repeated malaria on NK cell responses remains unclear. Here, we comprehensively profiled the NK cell response in a cohort of 264 Ugandan children. Repeated malaria exposure was associated with expansion of an atypical, CD56^neg population of NK cells that differed transcriptionally, epigenetically, and phenotypically from CD56^dim NK cells, including decreased expression of PLZF and the Fc receptor γ-chain, increased histone methylation, and increased protein expression of LAG-3, KIR, and LILRB1. CD56^neg NK cells were highly functional and displayed greater antibody-dependent cellular cytotoxicity than CD56^dim NK cells. Higher frequencies of CD56^neg NK cells were associated with protection against symptomatic malaria and high parasite densities. After marked reductions in malaria transmission, frequencies of these cells rapidly declined, suggesting that continuous exposure to Plasmodium falciparum is required to maintain this modified, adaptive-like NK cell subset.

Age-dependent changes in circulating Tfh cells influence development of functional malaria antibodies in children

T-follicular helper (Tfh) cells are key drivers of antibodies that protect from malaria. However, little is known regarding the host and parasite factors that influence Tfh and functional antibody development. Here, we use samples from a large cross-sectional study of children residing in an area of high malaria transmission in Uganda to characterize Tfh cells and functional antibodies to multiple parasites stages. We identify a dramatic re-distribution of the Tfh cell compartment with age that is independent of malaria exposure, with Th2-Tfh cells predominating in early childhood, while Th1-Tfh cell gradually increase to adult levels over the first decade of life. Functional antibody acquisition is age-dependent and hierarchical acquired based on parasite stage, with merozoite responses followed by sporozoite and gametocyte antibodies. Antibodies are boosted in children with current infection, and are higher in females. The children with the very highest antibody levels have increased Tfh cell activation and proliferation, consistent with a key role of Tfh cells in antibody development. Together, these data reveal a complex relationship between the circulating Tfh compartment, antibody development and protection from malaria.

Adults with Plasmodium falciparum malaria have higher magnitude and quality of circulating T-follicular helper cells compared to children

BACKGROUND

Protective malarial antibodies are acquired more rapidly in adults than children, independently of cumulative exposure, however the cellular responses mediating these differences are unknown. CD4 T-follicular helper (Tfh) cells have key roles in inducing antibodies, with Th2-Tfh cell activation associated with antibody development in malaria. Whether Tfh cell activation in malaria is age dependent is unknown and no studies have compared Tfh cell activation in children and adults with malaria.

METHODS

We undertook a comprehensive study of Tfh cells, along with B cells and antibody induction in children and adults with malaria. Activation and proliferation of circulating Tfh (cTfh) cell subsets was measured ex vivo and parasite-specific Tfh cell frequencies and functions studied with Activation Induced Marker (AIM) assays and intracellular cytokine staining.

FINDINGS

During acute malaria, the magnitude of cTfh cell activation was higher in adults than in children and occurred across all cTfh cell subsets in adults but was restricted only to the Th1-cTfh subset in children. Further, adults had higher levels of parasite-specific cTfh cells, and cTfh cells which produced more Th2-Tfh associated cytokine IL-4. Consistent with a role of higher Tfh cell activation in rapid immune development in adults, adults had higher activation of B cells during infection and higher induction of antibodies 7 and 28 days after malaria compared to children.

INTERPRETATION

Our data provide evidence that age impacts Tfh cell activation during malaria, and that these differences may influence antibody induction after treatment. Findings have important implications for vaccine development in children.

FUNDING

This word was supported by the National Health and Medical Research Council of Australia, Wellcome Trust, Charles Darwin University Menzies School of Health Research, Channel 7 Children's Research Foundation, and National Health Institute.

Safety, infectivity and immunogenicity of a genetically attenuated blood-stage malaria vaccine

BACKGROUND

There is a clear need for novel approaches to malaria vaccine development. We aimed to develop a genetically attenuated blood-stage vaccine and test its safety, infectivity, and immunogenicity in healthy volunteers. Our approach was to target the gene encoding the knob-associated histidine-rich protein (KAHRP), which is responsible for the assembly of knob structures at the infected erythrocyte surface. Knobs are required for correct display of the polymorphic adhesion ligand P. falciparum erythrocyte membrane protein 1 (PfEMP1), a key virulence determinant encoded by a repertoire of var genes.

METHODS

The gene encoding KAHRP was deleted from P. falciparum 3D7 and a master cell bank was produced in accordance with Good Manufacturing Practice. Eight malaria naïve males were intravenously inoculated (day 0) with 1800 (2 subjects), 1.8 × 10⁵ (2 subjects), or 3 × 10⁶ viable parasites (4 subjects). Parasitemia was measured using qPCR; immunogenicity was determined using standard assays. Parasites were rescued into culture for in vitro analyses (genome sequencing, cytoadhesion assays, scanning electron microscopy, var gene expression).

RESULTS

None of the subjects who were administered with 1800 or 1.8 × 10⁵ parasites developed parasitemia; 3/4 subjects administered 3× 10⁶ parasites developed significant parasitemia, first detected on days 13, 18, and 22. One of these three subjects developed symptoms of malaria simultaneously with influenza B (day 17; 14,022 parasites/mL); one subject developed mild symptoms on day 28 (19,956 parasites/mL); and one subject remained asymptomatic up to day 35 (5046 parasites/mL). Parasitemia rapidly cleared with artemether/lumefantrine. Parasitemia induced a parasite-specific antibody and cell-mediated immune response. Parasites cultured ex vivo exhibited genotypic and phenotypic properties similar to inoculated parasites, although the var gene expression profile changed during growth in vivo.

CONCLUSIONS

This study represents the first clinical investigation of a genetically attenuated blood-stage human malaria vaccine. A P. falciparum 3D7 kahrp- strain was tested in vivo and found to be immunogenic but can lead to patent parasitemia at high doses.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (number: ACTRN12617000824369 ; date: 06 June 2017).

Surface area-to-volume ratio, not cellular viscoelasticity, is the major determinant of red blood cell traversal through small channels

The remarkable deformability of red blood cells (RBCs) depends on the viscoelasticity of the plasma membrane and cell contents and the surface area to volume (SA:V) ratio; however, it remains unclear which of these factors is the key determinant for passage through small capillaries. We used a microfluidic device to examine the traversal of normal, stiffened, swollen, parasitised and immature RBCs. We show that dramatic stiffening of RBCs had no measurable effect on their ability to traverse small channels. By contrast, a moderate decrease in the SA:V ratio had a marked effect on the equivalent cylinder diameter that is traversable by RBCs of similar cellular viscoelasticity. We developed a finite element model that provides a coherent rationale for the experimental observations, based on the nonlinear mechanical behaviour of the RBC membrane skeleton. We conclude that the SA:V ratio should be given more prominence in studies of RBC pathologies.

Loss of complement regulatory proteins on red blood cells in mild malarial anaemia and in Plasmodium falciparum induced blood-stage infection

Background

Anaemia is a major consequence of malaria, caused by the removal of both infected and uninfected red blood cells (RBCs) from the circulation. Complement activation and reduced expression of complement regulatory proteins (CRPs) on RBCs are an important pathogenic mechanism in severe malarial anaemia in both Plasmodium falciparum and Plasmodium vivax infection. However, little is known about loss of CRPs on RBCs during mild malarial anaemia and in low-density infection.

Methods

The expression of CRP CR1, CD55, CD59, and the phagocytic regulator CD47, on uninfected normocytes and reticulocytes were assessed in individuals from two study populations: (1) P. falciparum and P. vivax-infected patients from a low transmission setting in Sabah, Malaysia; and, (2) malaria-naïve volunteers undergoing P. falciparum induced blood-stage malaria (IBSM). For clinical infections, individuals were categorized into anaemia severity categories based on haemoglobin levels. For IBSM, associations between CRPs and haemoglobin level were investigated.

Results

CRP expression on RBC was lower in Malaysian individuals with P. falciparum and P. vivax mild malarial anaemia compared to healthy controls. CRP expression was also reduced on RBCs from volunteers during IBSM. Reduction occurred on normocytes and reticulocytes. However, there was no significant association between reduced CRPs and haemoglobin during IBSM.

Conclusions

Removal of CRPs occurs on both RBCs and reticulocytes during Plasmodium infection even in mild malarial anaemia and at low levels of parasitaemia.

Multimodal analysis of Plasmodium knowlesi ‐infected erythrocytes reveals large invaginations, swelling of the host cell, and rheological defects

The simian parasite Plasmodium knowlesi causes severe and fatal malaria infections in humans, but the process of host cell remodelling that underpins the pathology of this zoonotic parasite is only poorly understood. We have used serial block‐face scanning electron microscopy to explore the topography of P. knowlesi‐infected red blood cells (RBCs) at different stages of asexual development. The parasite elaborates large flattened cisternae (Sinton Mulligan's clefts) and tubular vesicles in the host cell cytoplasm, as well as parasitophorous vacuole membrane bulges and blebs, and caveolar structures at the RBC membrane. Large invaginations of host RBC cytoplasm are formed early in development, both from classical cytostomal structures and from larger stabilised pores. Although degradation of haemoglobin is observed in multiple disconnected digestive vacuoles, the persistence of large invaginations during development suggests inefficient consumption of the host cell cytoplasm. The parasite eventually occupies ~40% of the host RBC volume, inducing a 20% increase in volume of the host RBC and an 11% decrease in the surface area to volume ratio, which collectively decreases the ability of the P. knowlesi‐infected RBCs to enter small capillaries of a human erythrocyte microchannel analyser. Ektacytometry reveals a markedly decreased deformability, whereas correlative light microscopy/scanning electron microscopy and python‐based skeleton analysis (Skan) reveal modifications to the surface of infected RBCs that underpin these physical changes. We show that P. knowlesi‐infected RBCs are refractory to treatment with sorbitol lysis but are hypersensitive to hypotonic lysis. The observed physical changes in the host RBCs may underpin the pathology observed in patients infected with P. knowlesi.

High resolution FTIR imaging provides automated discrimination and detection of single malaria parasite infected erythrocytes on glass

New highly sensitive tools for malaria diagnostics are urgently needed to enable the detection of infection in asymptomatic carriers and patients with low parasitemia. In pursuit of a highly sensitive diagnostic tool that can identify parasite infections at the single cell level, we have been exploring Fourier transform infrared (FTIR) microscopy using a Focal Plane Array (FPA) imaging detector. Here we report for the first time the application of a new optic configuration developed by Agilent that incorporates 25× condenser and objective Cassegrain optics with a high numerical aperture (NA = 0.81) along with additional high magnification optics within the microscope to provide 0.66 micron pixel resolution (total IR system magnification of 61×) to diagnose malaria parasites at the single cell level on a conventional glass microscope slide. The high quality images clearly resolve the parasite's digestive vacuole demonstrating sub-cellular resolution using this approach. Moreover, we have developed an algorithm that first detects the cells in the infrared image, and secondly extracts the average spectrum. The average spectrum is then run through a model based on Partial Least Squares-Discriminant Analysis (PLS-DA), which diagnoses unequivocally the infected from normal cells. The high quality images, and the fact this measurement can be achieved without a synchrotron source on a conventional glass slide, shows promise as a potential gold standard for malaria detection at the single cell level.

Disrupting assembly of the inner membrane complex blocks Plasmodium falciparum sexual stage development

Transmission of malaria parasites relies on the formation of a specialized blood form called the gametocyte. Gametocytes of the human pathogen, Plasmodium falciparum, adopt a crescent shape. Their dramatic morphogenesis is driven by the assembly of a network of microtubules and an underpinning inner membrane complex (IMC). Using super-resolution optical and electron microscopies we define the ultrastructure of the IMC at different stages of gametocyte development. We characterize two new proteins of the gametocyte IMC, called PhIL1 and PIP1. Genetic disruption of PhIL1 or PIP1 ablates elongation and prevents formation of transmission-ready mature gametocytes. The maturation defect is accompanied by failure to form an enveloping IMC and a marked swelling of the digestive vacuole, suggesting PhIL1 and PIP1 are required for correct membrane trafficking. Using immunoprecipitation and mass spectrometry we reveal that PhIL1 interacts with known and new components of the gametocyte IMC.

Transmission of the malaria parasite from humans to mosquitoes relies on the formation of the specialised blood stage gametocyte. Plasmodium falciparum gametocytes mature over about 10 days, during which time they undergo a remarkable morphological transformation, eventually adopting a characteristic crescent shape. The shape changes are thought to facilitate the mechanical sequestration of maturing gametocytes within the bone marrow and spleen, as well as the eventual release into the circulation. Failure to mature correctly leads to a failure to transmit. Despite the importance of this process, little is known about the molecular basis of elongation. In this work, we introduce 3D Electron Microscopy of P. falciparum gametocytes and use it, in a combination with super-resolution optical microscopy, to elucidate the genesis and expansion of the molecular structures that drive gametocyte elongation. We use protein interaction profiling to identify some of the proteins that help drive the shape change and employ inducible gene knockdown strategies to show that these proteins play a role in remodeling membranes, and are needed for gametocyte elongation. This work points to potential targets for the development of transmission-blocking therapies.

A portable microfluidic Aptamer-Tethered Enzyme Capture (APTEC) biosensor for malaria diagnosis

There is a critical need for better biosensors for the detection and diagnosis of malaria. We previously developed a DNA aptamer that recognises the Plasmodium falciparum lactate dehydrogenase (PfLDH) enzyme with high sensitivity and specificity. The aptamer was integrated into an Aptamer-Tethered Enzyme Capture (APTEC) assay as a laboratory-based diagnostic approach. However, a portable equipment-free point-of-care aptamer-mediated biosensor could have a significant impact on malaria diagnosis in endemic regions. Here, we present a new concept for a malaria biosensor whereby aptamers are coated onto magnetic microbeads for magnet-guided capture, wash and detection of the biomarker. A biosensor incorporating three separate microfluidic chambers was designed to enable such magnet-guided equipment-free colorimetric detection of PfLDH. A series of microfluidic biosensor prototypes were optimised to lower rates of inter-chamber diffusion, increase sensitivity, and provide a method for point-of-care sample testing. The biosensor showed high sensitivity and specificity when detecting PfLDH using both in vitro cultured parasite samples and using clinical samples from malaria patients. The high performance of the biosensor provides a proof-of-principle for a portable biosensor that could be adaptable for a variety of aptamer-mediated diagnostic scenarios.

Conformational dynamics and antigenicity in the disordered malaria antigen merozoite surface protein 2

Merozoite surface protein 2 (MSP2) of Plasmodium falciparum is an abundant, intrinsically disordered protein that is GPI-anchored to the surface of the invasive blood stage of the malaria parasite. Recombinant MSP2 has been trialled as a component of a malaria vaccine, and is one of several disordered proteins that are candidates for inclusion in vaccines for malaria and other diseases. Nonetheless, little is known about the implications of protein disorder for the development of an effective antibody response. We have therefore undertaken a detailed analysis of the conformational dynamics of the two allelic forms of MSP2 (3D7 and FC27) using NMR spectroscopy. Chemical shifts and NMR relaxation data indicate that conformational and dynamic properties of the N- and C-terminal conserved regions in the two forms of MSP2 are essentially identical, but significant variation exists between and within the central variable regions. We observe a strong relationship between the conformational dynamics and the antigenicity of MSP2, as assessed with antisera to recombinant MSP2. Regions of increased conformational order in MSP2, including those in the conserved regions, are more strongly antigenic, while the most flexible regions are minimally antigenic. This suggests that modifications that increase conformational order may offer a means to tune the antigenicity of MSP2 and other disordered antigens, with implications for vaccine design.

Somatosensory evoked potentials show plastic changes following a novel motor training task with the thumb

OBJECTIVE

Accumulating evidence indicates that plastic changes can be maladaptive in nature, resulting in movement and neurological disorders. The aim of this study was to further the understanding of these neurophysiological changes in sensorimotor integration (SMI) using somatosensory evoked potentials (SEPs) and concurrent performance changes following a repetitive typing task.

METHODS

SEPs were recorded following median nerve stimulation at the wrist and performed pre and post intervention. 24 participants were randomly assigned to either an intervention group which performed a 20min repetitive typing task or a control group which participated in a 20min period of mental recitation.

RESULTS

The P22-N24 amplitude increased by 59.6%, compared to only 0.96% increase following the control. The P22-N30 SEP peak amplitude increased on average 13.4% following the motor training, compared to only 0.92% following the control. Significant improvement in reaction time when comparing performance of the motor task for the intervention group was observed.

CONCLUSIONS

The N24 increase supports the involvement of cerebellar connections and the N30 increase provides further support for changes in SMI following motor learning.

SIGNIFICANCE

Combining motor training tasks with electrophysiological techniques gives insight into the mechanisms of disordered SMI and whether the changes are adaptive or maladaptive.

A comparison of the effects of a chlamydial vaccine administered during or after a C. muridarum urogenital infection of female mice

Research into an efficacious Chlamydia trachomatis vaccine is ongoing, however, there has been no examination into the timing of vaccine administration to either asymptomatically or previously infected individuals. Using the female Chlamydia muridarum genital tract mouse model, we examined this aspect of vaccine development. Our results show timing of vaccination affected the production of systemic antibodies, but had minimal effects on mucosal antibody production. Vaccination during an active infection or after a resolved infection did not provide protection against re-exposure to Chlamydia, and did not exacerbate the development of pathological sequelae in infected mice. This demonstrates that vaccination may not be protective in individuals who are seropositive for an acute or previous chlamydial infection.

A quantitative and morphological study of projection neurons in lamina I of the rat lumbar spinal cord

In the rat lumbar spinal cord the major supraspinal targets for lamina I projection neurons are the caudal ventrolateral medulla (CVLM), lateral parabrachial area (LPb) and periaqueductal grey matter (PAG). In this study we have estimated the number of lamina I neurons retrogradely labelled from each of these sites in the L4 segment, as well as the proportion that can be labelled by injecting different tracers into two separate sites. Our results suggest that this segment contains approximately 400 lamina I projection neurons on each side, and that approximately 85% of these can be labelled from either the CVLM or the LPb on the contralateral side. Around 120 lamina I cells in L4 project to the PAG, and over 90% of these cells can also be labelled from the CVLM or LPb. Most lamina I neurons projecting to CVLM or LPb are located in the contralateral dorsal horn, but in each case some cells were found to have bilateral projections. We also examined horizontal sections to investigate morphology and the expression of the neurokinin 1 (NK1) receptor in cells labelled from CVLM, LPb or PAG. There were no consistent morphological differences between these groups, however, while cells with strong or moderate NK1 receptor-immunostaining were labelled from LPb or CVLM, they seldom projected to the PAG. These results suggest that many lamina I cells project to more than one site in the brain and that those projecting to PAG may represent a distinct subclass of lamina I projection neuron.

Properties of single nerve fibres that evoke blood flow changes in cat dental pulp

Single nerve fibres innervating tooth pulp were isolated from filaments dissected from the inferior alveolar nerve in 17 anaesthetized cats. The fibres were studied to determine whether electrical stimulation of single units produced detectable changes in pulpal blood flow. Single pulpal nerve fibres were electrically stimulated at just above their thresholds and blood flow was recorded with a laser-Doppler flow meter from the pulp of the ipsilateral canine. The thresholds of single fibres in dissected filaments were determined either by recording antidromic action potentials from the tooth or by using a novel technique based on collision. Units that produced blood flow changes were further characterized by recording their response to hot, cold, osmotic and hydrostatic pressure, and mechanical stimulation of exposed dentine and to drying the dentine. Of 93 units isolated, 14 produced changes in pulpal blood flow when stimulated electrically at 1 or 10 Hz. All had conduction velocities (0.8-2.0 m s(-1)) in the C-fibre range. Ten produced vasodilatation and the remaining four, vasoconstriction. Five of the fibres that produced vasodilatation also responded to the hot stimulus, suggesting that they may form part of an axon reflex or similar mechanism. The four vasoconstrictor units did not respond to any form of stimulus other than electrical and were presumed to be sympathetic post-ganglionic fibres.

Responses of spinothalamic lamina I neurons to maintained noxious mechanical stimulation in the cat

Noxious mechanical stimuli that are maintained for minutes produce a continuous sensation of pain in humans that augments during the stimulus. It has recently been shown with systematic force-controlled stimuli that, while all mechanically responsive nociceptors adapt to these stimuli, the basis for such pain can be ascribed to A-fiber rather than C-fiber nociceptors, based on distinctions in their respective response profiles and stimulus-response functions. The present experiments investigated whether similar distinctions could be made in subsets of nociceptive lamina I spinothalamic tract (STT) neurons using similar maintained stimuli. Twenty-eight lamina I STT neurons in the lumbosacral dorsal horn of barbiturate-anesthetized cats were tested with noxious mechanical stimuli applied with a probe of 0.1 mm(2) contact area at forces of 25, 50, and 100 g for 2 min. The neurons were classified as nociceptive-specific (NS, n = 14) or polymodal nociceptive (HPC, n = 14) based on their responses to quantitative thermal stimuli. The NS neurons had greater responses and showed less adaptation than the HPC neurons in response to these stimuli, and they encoded stimulus intensity better. Comparison of the normalized response profiles of all 28 nociceptive lamina I STT neurons, independent of cell classification, revealed 2 subgroups that differed significantly: "Maintained" cells with responses that remained above 50% of the initial peak rate during stimulation and "Adapting" cells with responses that quickly declined to <50%. The Maintained neurons encoded the intensity of the mechanical stimuli better than the Adapting neurons, based on ratiometric functions. A k-means cluster analysis of all 28 cells distinguished the identical two subgroups. These categories corresponded closely to the NS and HPC categories: Maintained cells were mostly NS neurons (10 NS, 3 HPC), and Adapting cells were mostly HPC neurons (4 NS, 11 HPC). Thus the present data are consistent with the distinctions between A-fiber and C-fiber nociceptors observed previously, because A-fiber nociceptors are the predominant input to NS lamina I STT neurons and C-fiber nociceptors are the predominant input to HPC neurons. These findings support the view that NS, but perhaps not HPC, lamina I STT neurons have a role in the pain caused by maintained mechanical stimuli and contribute to the sensations of "first" pain and "sharpness." Nonetheless, none of the units studied showed increasing responses during the stimuli, suggesting a role for other ascending neurons or forebrain integration in the augmenting pain produced by maintained mechanical stimulation.

Responses of spinothalamic lamina I neurons to repeated brief contact heat stimulation in the cat

It was recently shown that repeated heat stimulation, using brief contacts (<1 s) with a preheated thermode at sufficiently short interstimulus intervals (ISIs <5 s) and high temperatures (> or =51 degrees C), will elicit in humans a sensation of rapidly augmenting "second" (burning) pain with only a weak "first" (sharp) pain sensation. Most strikingly, at short intertrial intervals (ITIs >5 s) such summation will reset, or begin again at baseline. In the present experiments, the responses of nociceptive lamina I spinothalamic (STT) neurons in the lumbosacral dorsal horn of barbiturate-anesthetized cats were examined using this repeated brief contact heat paradigm. The neurons were classified as nociceptive-specific (NS, n = 8) or polymodal nociceptive (HPC, n = 8) based on their responses to quantitative thermal stimuli; all had receptive fields on the glabrous ventral hindpaw. A pneumatic piston was used to apply a thermode preheated to 34, 46, 49, 53, or 58 degrees C with a contact dwell time of approximately 0.7 s to the ventral hindpaw repeatedly (15 times) at ISIs of 2, 3, and 5 s, with 3-5 min between trials. The mean responses of the 16 nociceptive lamina I STT cells showed rapid temporal summation that was directly dependent on temperature and inversely dependent on ISI, with the greatest increases occurring between the 3rd and 10th contacts. The temporal profiles of this family of curves correspond with the psychophysical data on human sensation. Further analysis showed that this summation was due to the HPC cells, which all showed strong summation; in contrast, the NS cells showed little, if any. The HPC responses to the repeated heat stimuli lagged each contact by approximately 1 s, consistent with the strong, monosynaptic C-fiber input that is characteristic of HPC cells and also with the dependence of second pain on C-fiber nociceptors. HPC cells also displayed the reset phenomenon at short ITIs, again in correspondence with the psychophysical data. The summation and the reset displayed by HPC cells were not related to skin temperature. Thus the results presented in this study, together with those in the preceding article, demonstrate a double dissociation indicating that NS and HPC lamina I STT cells can subserve the qualitatively distinct sensations of first (sharp) and second (burning) pain, respectively. These findings support the concept that the lamina I STT projection comprises several discrete sensory channels that are integrated in the forebrain to generate distinct sensations.

Activation of spinobulbar lamina I neurons by static muscle contraction

Spinal lamina I neurons are selectively activated by small-diameter somatic afferents, and they project to brain stem sites that are critical for homeostatic control. Because small-diameter afferent activity evoked by contraction of skeletal muscle reflexly elicits exercise-related cardiorespiratory activation, we tested whether spinobulbar lamina I cells respond to muscle contraction. Spinobulbar lamina I neurons were identified in chloralose-anesthetized cats by antidromic activation from the ipsilateral caudal ventrolateral medulla. Static contractions of the ipsilateral triceps surae muscle were evoked by tibial nerve stimulation using parameters that avoid afferent activation, and arterial blood pressure responses were recorded. Recordings were maintained from 13 of 17 L(7) lamina I spinobulbar neurons during static muscle contraction, and 5 of these neurons were excited. Three were selectively activated only by muscle afferents and did not have a cutaneous receptive field. Spinobulbar lamina I neurons activated by muscle contraction provide an ascending link for the reflex cardiorespiratory adjustments that accompany muscular work. This study provides an important first step in elucidating an ascending afferent pathway for somato-autonomic reflexes.

Spinothalamic lamina I neurones selectively responsive to cutaneous warming in cats

1. In order to further characterize the role of lamina I as the source of central ascending neural pathways for thermoreception and thermoregulation, experiments were performed on anaesthetized cats to determine the quantitative response characteristics of warming-specific lumbosacral spinothalamic lamina I neurones. 2. We identified 10 neurones out of 474 that were selectively excited by cutaneous warming (Warm cells). Their thresholds were all in the range 35-37 degrees C at a baseline of 34.5 degrees C, and their discharge linearly encoded the temperature of graded, innocuous warming stimuli with a sensitivity of 2.1 Hz x degrees C(-1). 3. The stimulus-response function of the Warm cells plateaued at temperatures that were in the noxious heat range. 4. The Warm cells were distinguished from other classes of spinothalamic lamina I neurones by their peripheral inputs, central conduction velocities and level of ongoing activity. 5. The discharge of Warm cells compares well with the known human psychophysics of warm sensibility, and these neurones are likely to be crucial to discriminative thermoreception. Additionally, a role in thermoregulation, a defining feature of mammalian homeostasis, is suggested.

Age-associated thymic atrophy is not associated with a deficiency in the CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) thymocyte population

Age-associated thymic atrophy has been proposed to be due to changes in both the thymic microenvironment and in the intrinsic properties of the early T cell progenitors, the CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) cells. We have purified these cells from the thymus of both old and young mice and demonstrate no age-associated defect in their ability to differentiate into their progeny in vitro when used to reconstitute fetal thymic organ cultures. We also demonstrate that in the presence of anti-IL-7, CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) cells from young mice show reduced thymocyte development in fetal thymic organ cultures compared with controls. Finally we have shown that old mice treated with IL-7 show improved thymopoiesis compared with control groups. The increased thymopoiesis seen in the old animals occurs in the sequential manner which would be anticipated for an agent working directly on the early stages, including the CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) cells.

Quantitative response characteristics of thermoreceptive and nociceptive lamina I spinothalamic neurons in the cat

The physiological characteristics of antidromically identified lamina I spinothalamic (STT) neurons in the lumbosacral spinal cord were examined using quantitative thermal and mechanical stimuli in barbiturate-anesthetized cats. Cells belonging to the three main recognized classes were included based on categorization with natural cutaneous stimulation of the hindpaw: nociceptive-specific (NS), polymodal nociceptive (HPC), or thermoreceptive-specific (COOL) cells. The mean central conduction latencies of these classes differed significantly; NS = 130.8 +/- 55.5 (SD) ms (n = 100), HPC = 72.1 +/- 28.0 ms (n = 128), and COOL = 58.6 +/- 25.3 ms (n = 136), which correspond to conduction velocities of 2.5, 4.6, and 5.6 m/s. Based on recordings made prior to any noxious stimulation, the mean spontaneous discharge rates of these classes also differed: NS = 0.5 +/- 0.7 imp/s (n = 47), HPC = 0.9 +/- 0.7 imp/s (n = 59), and COOL = 3.3 +/- 2.6 imp/s (n = 107). Standard, quantitative, thermal stimulus sequences applied with a Peltier thermode were used to characterize the stimulus-response functions of 76 COOL cells, 47 HPC cells, and 37 NS cells. The COOL cells showed a very linear output from 34 degrees C down to approximately 15 degrees C and a maintained plateau thereafter. The HPC cells showed a fairly linear but accelerating response to cold below a median threshold of approximately 24 degrees C and down to 9 degrees C (measured at the skin-thermode interface with a thermode temperature of 2 degrees C). The HPC cells and the NS cells both showed rapidly increasing, sigmoidal response functions to noxious heat with a fairly linear response between 45 and 53 degrees C, but they had significantly different thresholds; half of the HPC cells were activated at ~45.5 degrees C and half of the NS cells at approximately 43 degrees C. The 20 HPC lamina I STT cells and 10 NS cells tested with quantitative pinch stimuli showed fairly linear responses above a threshold of approximately 130 g/mm(2) for HPC cells and a threshold of approximately 100 g/mm(2) for NS cells. All of these response functions compare well (across species) with the available data on the characteristics of thermoreceptive and nociceptive primary afferent fibers and the appropriate psychophysics in humans. Together these results support the concept that these classes of lamina I STT cells provide discrete sensory channels for the sensations of temperature and pain.

Bromelain modulates T cell and B cell immune responses in vitro and in vivo

The ability to modulate immune responses is a major aim of many vaccine and immunotherapeutic development programs. Bromelain, a mixture of cysteine proteases, modulates immunological responses and has been proposed to be of clinical use. However, the identity of the immune cells affected by bromelain and the specific cellular functions that are altered remain poorly understood. To address these shortcomings in our knowledge, we have used both in vitro and in vivo immunological assays to study the effects of bromelain. We found that bromelain enhanced T cell receptor (TCR) and anti-CD28-mediated T cell proliferation in splenocyte cultures by increasing the costimulatory activity of accessory cell populations. However, despite increased T cell proliferation, bromelain concomitantly decreased IL-2 production in splenocyte cultures. Additionally, bromelain did not affect TCR and CD28-induced proliferation of highly purified CD4+ T cells, but did inhibit IL-2 production by these cells. In vivo, bromelain enhanced T-cell-dependent, Ag-specific, B cell antibody responses. Again, bromelain induced a concomitant decrease in splenic IL-2 mRNA accumulation in immunized mice. Together, these data show that bromelain can simultaneously enhance and inhibit T cell responses in vitro and in vivo via a stimulatory action on accessory cells and a direct inhibitory action on T cells. This work provides important insights into the immunomodulatory activity of bromelain and has important implications for the use of exogenous cysteine proteases as vaccine adjuvants or immunomodulatory agents.

Bromelain activates murine macrophages and natural killer cells in vitro

The innate immune response is critical for effective immunity against most pathogens. In this study, we show that bromelain, a mixture of cysteine proteases, can enhance IFN-gamma-mediated nitric oxide and TNFalpha production by macrophages. Bromelain's effect was independent of endotoxin receptor activation and was not caused by direct modulation of IFN-gamma receptors. Instead, bromelain either enhanced or acted synergistically with IFN-gamma receptor-mediated signals. These effects were seen in both RAW 264.7, a macrophage cell line, and primary macrophage populations. Bromelain also increased IL-2- and IL-12-mediated IFN-gamma production by NK cells. These results indicate a potential role for bromelain in the activation of inflammatory responses in situations where they may be deficient, such as may occur in immunocompromised individuals.

T cell phenotypes of the normal nasal mucosa: induction of Th2 cytokines and CCR3 expression by IL-4

Mucosal environments such as that of the nose are points of first contact between the human organism and its environment. At these sites the immune system must be regulated to differentiate between and respond appropriately to pathogens and harmless contaminants. T cell-driven immune responses broadly fall into Th1- or Th2-type phenotypes, with increasing evidence that the recruitment of these T lymphocyte subsets is mediated by selective expression of specific chemokine receptors. We have investigated the immunology of the normal nasal mucosa. We show that nasal T cell lines from normal individuals, expanded by culture in IL-2, show reduced expression of the Th2-type cytokines IL-4 and IL-5 compared with lines derived from the blood of the same subjects. These T cells also show reduced expression of the Th2-selective chemokine receptor, CCR3, but similar levels of CCR4 compared with the blood-derived lines. This apparent suppression of Th2 cytokine and CCR3 expression by nasal T cells was reversed by addition of IL-4 to the culture medium. These data are consistent with the presence of a nasal mucosal microenvironment that suppresses Th2 responses and may represent a protective measure against atopic allergic disease in humans and a favoring of Th1 responses to infectious agents. In contrast, T cell expression of CCR1 was higher in the nose than in the blood regardless of the culture medium cytokine environment in keeping with a role for this receptor in tissue homing or lymphocyte activation.

Il-7 and not stem cell factor reverses both the increase in apoptosis and the decline in thymopoiesis seen in aged mice

Thymic atrophy is an age-associated decline in commitment to the T cell lineage considered to be associated with defective TCR beta-chain rearrangement. Both IL-7 and stem cell factor (SCF) have dominant roles at this stage of triple negative (TN) thymocyte development. Because there is no age-associated decrease in the number of CD44(+)CD25(-)CD3(-)CD4(-)CD8(-) cells, this study investigated whether alterations in apoptosis within the TN pathway accounted for diminishing thymocyte numbers with age. Here we show significant age-associated increases in apoptotic TN thymocytes, specifically within CD44(+)CD25(+) and CD44(-)CD25(+) subpopulations, known to be the location of TCR beta-chain rearrangement. IL-7 added to TN cultures established from old mice significantly both reduces apoptosis and increases the percentage of live cells within CD44(+)CD25(+) and CD44(-)CD25(+) subpopulations after 24 h, with prosurvival effects remaining after 5 days. SCF failed to demonstrate prosurvival effects in old or young cultures, and IL-7 and SCF together did not improve upon IL-7 alone. IL-7R expression did not decline with age, ruling out the possibility that the age-associated increase in apoptosis was attributed to reduced IL-7R expression. Compared with PBS, treatment of old mice with IL-7 produced significant increases in live TN cells. By comparison, treatment with SCF failed to increase live TN numbers, and IL-7 and SCF together failed to significantly improve thymopoiesis above that shown by IL-7 alone. Thus, treatment with IL-7 alone can reverse the age-associated defect in TN thymocyte development revealed by in vitro studies to be located at the stages of TCR beta-chain rearrangement.

Spinothalamic lamina I neurons selectively sensitive to histamine: a central neural pathway for itch

We found a class of lamina I spinothalamic tract (STT) neurons selectively excited by iontophoretic histamine. The responses of this class of neurons parallel the pure itching sensation this stimulus elicits in humans, and match the responses of peripheral C-fibers that have similar selectivity. These neurons have distinct central conduction velocities and thalamic projections, indicating that they constitute a unique subset of STT neurons. These findings can explain why a lesion of the lateral STT disrupts itch along with pain and temperature sensations. Our findings provide strong evidence that itch is subserved by specific neural elements both peripherally and centrally.

Gender-related differences in the rates of age associated thymic atrophy

Age associated thymic atrophy has been shown to be linked to problems with rearrangement of the beta chain of the T cell receptor (TCR) in male mice during the early phases of the intrathymic T cell developmental pathway. In this study, thymic atrophy in female mice was found to occur at a different rate than in male mice. At 9 months of age there was a significantly greater number of cells in the thymus of female mice compared with male mice, with the major difference found in the CD4+CD8+ populations. The thymii of female mice at 9 months of age contained double the number of these cells compared with male mice. Analysis of the CD4+CD8+ cells at 9 months of age demonstrated increased numbers of cells expressing higher levels of CD3 in females compared with males indicating that in females more of these cells were producing successful alphabetaTCR pairings. In F5 transgenic mice comparison of the CD4+CD8+ population revealed no significant difference in their absolute numbers at 9 months of age. These results indicate that the gender differences at this time point were due to fewer permitted divisions prior to the expression of a selectable TCR alpha chain within the CD4+CD8+ populations in male compared with female mice. This gender difference was not due to the action of testosterone and unlikely to be due to differences in the level of oestrogen. The potential mechanisms of this difference may be related to a regulatory feedback of peripheral T cells on the developing thymocyte populations. Such age related changes in the numbers of cells within distinct thymic subpopulations leads to the possibility that the potential repertoire in females is greater than in males later in life.

A simple method for the measurement of sjTREC levels in blood

We have developed a relatively rapid, safe and simple method for the quantification of sjTREC levels in samples of peripheral blood. The assay uses an image analysis package to measure the brightness of PCR product bands on an image of the standard agarose gel. Comparison of the brightness of the band with that obtained from a standard curve provides a read-out of the amount of sjTRECs in the sample. We have compared the sjTREC levels we obtained with this method with those obtained from real time analysis PCR using a Lightcycler and found that they are comparable.

Displacement of the contents of dentinal tubules and sensory transduction in intradental nerves of the cat

Experiments were performed on anaesthetized cats to test the hypothesis that fluid flow through dentinal tubules is part of the mechanism involved in the transduction of pain-producing stimuli in teeth. In 11 animals, fluid flow through dentine and single- and multi-unit activity in intradental nerves were recorded simultaneously during the application of changes in hydrostatic pressure (-500 to +500 mm Hg) to exposed dentine. Seventeen A-fibres (conduction velocity (CV), 10.6-55.1 m s(-1)) were isolated that were pressure sensitive. The thresholds of these units in terms of dentinal fluid flow were in the range 0.3-2.1 nl s(-1) mm(-2) during outward flow from the pulp and 2.0-3.5 nl s(-1) mm(-2) during inward flow. All the units were more sensitive to outward than inward flow. Twenty-eight units (CV, 0.6-48.8 m s-1) were not pressure sensitive, and 12 of these had conduction velocities in the C-fibre range (< 2.5 m s(-1)). The velocities of the tubular contents were calculated by estimating the number and diameters of dentinal tubules exposed. At the threshold of single-fibre responses these velocities were in the range 31.7-222.9 microm s(-1) during outward flow 211.4-369.6 microm s-1 during inward flow. Repetitive pressure stimulation of dentine resulted in a progressive reduction in the evoked discharge, which was probably due to pulp damage. In seven animals, 10 single intradental nerve fibres were selected that responded to hydrostatic pressure stimuli and their responses to the application of hot, cold, osmotic, mechanical and drying stimuli to exposed dentine were investigated. With these stimuli dentinal fluid flow could not be recorded in vivo for technical reasons and was therefore recorded in vitro after completion of the electrophysiological recordings. With each form of stimulus, the discharge evoked in vivo was closely related to the flow predicted from the in vitro measurements. The results were therefore consistent with the hypothesis that the stimuli act through a common transduction mechanism that involves fluid flow through dentine.

Thymic involution in aging

The size of the naive T-cell pool is governed by output from the thymus and not by replication. This pool contributes cells to the activated/memory T-cell pool whose size can be increased through cell multiplication; both pools together constitute the peripheral T-cell pool. Aging is associated with involution of the thymus leading to a reduction in its contribution to the naive T-cell pool; however, despite this diminished thymic output, there is no significant decline in the total number of T cells in the peripheral T-cell pool. There are, however, considerable shifts in the ratios of both pools of cells, with an increase in the number of activated/memory T cells and the accumulation in older individuals of cells that fail to respond to stimuli as efficiently as T cells from younger individuals. Aging is also associated with a greater susceptibility to some infections and some cancers. An understanding of the causal mechanism of thymic involution could lead to the design of a rational therapy to reverse the loss of thymic tissue, renew thymic function, increase thymic output, and potentially improve immune function in aged individuals.

Prospective study of human betaherpesviruses after renal transplantation: association of human herpesvirus 7 and cytomegalovirus co-infection with cytomegalovirus disease and increased rejection

BACKGROUND

Human herpesvirus 6 (HHV-6) and HHV-7 are two lymphotropic herpesviruses, which, like cytomegalovirus (CMV), have the potential to be pathogenic in immunocompromised individuals. We have conducted a prospective investigation to compare the natural history of HHV-6 and HHV-7 infection with that of CMV after renal transplantation.

METHODS

Polymerase chain reaction was used to identify infections and quantify the viral load of CMV, HHV-6, and HHV-7 in peripheral blood samples from 52 renal transplant recipients. Betaherpesvirus infections were related to defined clinical criteria obtained by detailed examination of the clinical records of each patient for the immediate 120-day posttransplant period.

RESULTS

CMV was the most commonly detected virus after transplant (58% of patients), followed by HHV-7 (46%) and HHV-6 (23%). Examining the time to first polymerase chain reaction positivity, HHV-7 infection was detected earlier than CMV (P=0.05). The median maximum CMV viral load was significantly higher than those for HHV-6 (P=0.01) and HHV-7 (P<0.0001) and a trend for HHV-7 viral load to be greater than HHV-6 (P=0.08). Clinicopathological analyses revealed that, in those patients with rejection, HHV-7 was associated with more episodes of rejection (P=0.02). In addition, there was a significant increase in CMV disease occurring in patients with CMV and HHV-7 co-infection compared to those with CMV infection only (P=0.04).

CONCLUSIONS

HHV-7 should be further investigated as a possible co-factor in the development of CMV disease in renal transplant patients and may potentially exacerbate graft rejection. No clear pathological role was observed for HHV-6.

Thymic atrophy in the mouse is a soluble problem of the thymic environment

Age related deterioration in the function of the immune system has been recognised in many species. The clinical presentations of such immune dysfunction are an age-related increased susceptibility to certain infections, and an increased incidence of autoimmune disease and certain cancers. Laboratory investigations reveal a reduced ability of the cells from older individuals, compared with younger individuals, to perform in functional in vitro assays. These manifestations are thought to be causally linked to an age associated involution of the thymus, which precedes the onset of immune dysfunction. Hypotheses to account for the age-related changes in the thymus include: (i) an age related decline in the supply of T cell progenitors from the bone marrow (ii) an intrinsic defect in the marrow progenitors, or (iii) problems with rearrangement of the TCR beta chain because of a defect in the environment provided by the thymus. We have analysed these possible options in normal mice and also in mice carrying a transgenic T cell receptor. The results from these studies reveal no age related decline either in the number of function of T cell progenitors in the thymus, but changes in the thymic environment in terms of the cytokines produced. We have shown that specific cytokine replacement therapy leads to an increase in thymopoiesis in old animals.

Immunosenescence: potential causes and strategies for reversal

Age-related deterioration in immune function has been recognized in many species. In humans the clinical manifestation of such immune dysfunction is age-related increases in the susceptibility to certain infections and in the incidence of some autoimmune disease and certain cancers. Laboratory investigations reveal age-related changes in the peripheral T cell pool, in the predominant phenotype, cytokine production profiles, signalling function and in replicative ability following stimulus with antigen, mitogens or anti-CD3 antibody. These changes in the properties of peripheral T cells are thought to be causally linked to an age-associated involution in the thymus. Our analysis reveals that thymic involution is due to a change in the thymic microenvironment linked to a reduction in the level of available interleukin 7. Treatment with interleukin 7 leads to a reversal of thymic atrophy with increased thymopoiesis. This provides the potential to reverse the immune dysfunction seen in the peripheral T cell pool by replacing old cells with new output generated in the thymus. Problems to overcome in order for such an experimental therapy to be successful require careful analysis in order to provide an optimal strategy to ensure that new T cell emigrants from the thymus have a broad range of specificities and are able to enter the peripheral T cell pool.

Peripheral coding of tonic mechanical cutaneous pain: comparison of nociceptor activity in rat and human psychophysics

These experiments investigated temporal summation mechanisms of tonic cutaneous mechanical pain. Human volunteers provided psychophysical estimates of pain intensity, which were compared with discharge patterns of rat cutaneous nociceptors tested with identical stimulus protocols. Human subjects made either intermittent or continuous ratings of pain intensity during stimulation of the skin between the thumb and first finger. Stimulus intensities of 25, 50, and 100 g were applied with a probe of contact area of 0.1 mm(2) for 2 min. Pain perception significantly increased during stimulation (temporal summation) for the 50- and 100-g stimulus intensities. Sequential conduction block of the myelinated fibers supplying the stimulated skin was used to investigate the role of A-fiber mechanoreceptors and nociceptors in this temporal summation. Conduction block of the Abeta fibers resulted in an increase in mechanically evoked pain estimates and an increase in temporal summation, consistent with loss of Abeta-mediated inhibition. When only conduction in the unmyelinated fibers remained, pain estimates were reduced to the preblock levels, but temporal summation was still present. Electrophysiological recordings were made from filaments of the sciatic nerve supplying receptors in the plantar skin of barbiturate-anesthetized rats. Forty units fulfilled the identification criteria for nociceptors: 20 A-fiber and 20 C-fiber nociceptors. Each unit was characterized by recording its responses to graded mechanical and heat stimuli. Nociceptors were also tested with stimuli identical to those applied to the human subjects. The responses of all units to sustained mechanical stimuli were adaptive-that is, they exhibited a gradual decline in response with time. However, the time course of adaptation varied among units. All the C-fiber nociceptors and one-half of the A-fiber nociceptors had rapidly adapting responses. The remainder of the A-fibers displayed slowly adapting responses. One-third of all units also showed short-duration increases in firing rate during stimulation. The latency after stimulus onset of this rate acceleration was inversely related to stimulus intensity. Despite the apparent disparity between perceptual temporal summation and nociceptor adaptation, central and peripheral mechanisms are proposed that can reconcile the relationship between nociceptor activity and pain perception.

Mechanical and heat sensitization of cutaneous nociceptors after peripheral inflammation in the rat

Tissue injuries commonly cause an increase in pain sensitivity, so that normally painful stimuli become more painful (hyperalgesia), and those usually associated with nonnoxious sensations evoke pain (allodynia). The neural bases for these sensory phenomena have been explored most extensively using heat injuries and experimental arthritis as models. Heat sensitization of cutaneous nociceptors is observed after burns, and sensitization of articular afferents to limb movements occurs after knee joint inflammation. These are likely to be peripheral mechanisms of hyperalgesia. Others, using different models of peripheral inflammation, have only rarely found mechanical sensitization of cutaneous nociceptors. In general these studies have failed to evaluate suprathreshold mechanical sensitivity, which has led to the concept of enhanced spinal cord processing ("central sensitization") serving as the neural substrate for mechanical hyperalgesia. In the current experiments, the mechanical and heat responses of cutaneous nociceptors supplying the glabrous skin of the rat hindpaw were studied 16-24 h after induction of acute inflammation with complete Freund's adjuvant. Single-fiber recordings were made from nociceptors in the sciatic nerve of barbiturate-anesthetized animals, and their responses compared with those obtained from nociceptors tested identically in normal animals. Nociceptors were characterized by the following: 1) graded mechanical stimuli (5-90 g) delivered with probes of tip area of 1 and 0.1 mm(2), 2) their adaptive responses to 2-min mechanical stimuli at three intensities, and 3) their responses to graded heat stimuli (40-50 degrees C). Forty-three nociceptors were studied in the inflamed state; 20 were A fibers, and the remainder were C fibers. Mechanical thresholds, determined with calibrated monofilaments, were not significantly different from controls. Sensitization to suprathreshold mechanical stimuli was observed for both A- and C-fiber nociceptors, although it was greater for the A fibers. Similarly, sensitization during testing of adaptive properties of A- and C-fiber nociceptors was seen, although it was limited to the dynamic (initial) and not the static (plateau) phase of the response. Heat sensitization was observed in 25% of A-fiber nociceptors, but the responses of C fibers to heat were depressed. Other indicators of neuronal sensitization, such as spontaneous activity and expanded receptive fields, were also observed. It was concluded that the mechanical hyperalgesia caused by peripheral inflammation could be explained by nociceptor sensitization. Central mechanisms cannot be completely ruled out as contributing to such hyperalgesia, although their role may be much smaller than previously envisaged.

Longitudinal variation in hepatitis C virus (HCV) viraemia and early course of HCV infection after liver transplantation for HCV cirrhosis: the role of different immunosuppressive regimens

BACKGROUND

The role of the type of immunosuppression in the natural history of post-transplant hepatitis C virus (HCV) infection is unclear.

AIMS

To evaluate the fluctuation of HCV viraemia and the early course of infection, and their relation to the type of immunosuppression in HCV transplant patients.

METHODS

In 47 HCV transplant patients, serum HCV RNA levels were determined pretransplant and at one and two weeks, and three and 12 months after transplant. Initial immunosuppression was triple (cyclosporin, azathioprine, prednisolone) in 31, double (cyclosporin, prednisolone) in five, and single (cyclosporin or tacrolimus) in 11 patients. Prednisolone was withdrawn at a median of six months.

RESULTS

At three months, HCV RNA levels were higher in patients with single than with triple or double initial therapy. At 12 months, HCV RNA levels correlated only with duration of prednisolone treatment and were relatively higher in patients with triple compared with single initial immunosuppression. A higher necroinflammatory activity at 12 months post-transplant was found in patients with post-transplant acute hepatitis compared with those without. Extent of fibrosis at 12 months was associated with the 12 month HCV RNA level and occurrence of post-transplant acute hepatitis.

CONCLUSIONS

HCV RNA levels at three months after transplant are higher in patients treated with single initial immunosuppressive therapy, but at 12 months are higher in patients with longer duration of steroid treatment. HCV viraemia at 12 months seems to be particularly important, as its levels are strongly correlated with the severity of fibrosis.

Modality-specific hyper-responsivity of regenerated cat cutaneous nociceptors

1. Experiments were performed on anaesthetized cats to investigate the receptive properties of regenerated cutaneous tibial nerve nociceptors, and to obtain evidence for coupling between them and other afferent fibres as being possible peripheral mechanisms involved in neuropathic pain. These properties were studied 6-7 months after nerve section and repair. 2. Recordings were made from 25 regenerated nociceptors; 14 were A fibres and the remainder were C fibres. Their receptive field sizes and conduction velocities were similar to controls. There was no significant difference between their mechanical thresholds and those of a control population of nociceptors. 3. Regenerated nociceptors were significantly more responsive to suprathreshold mechanical stimuli than were uninjured control fibres. This increase in mechanical sensitivity occurred in both A and C fibres, although A fibres showed a greater increase in mechano-sensitivity than C fibres. Over half of the regenerated nociceptors (13/25) showed after-discharge to mechanical stimuli which was never seen in controls; the mean firing rate during this period of after-discharge was significantly related to both stimulus intensity and stimulus area. 4. There was no significant difference between the heat encoding properties of regenerated nociceptors and control nociceptors. Cold sensitivity was similarly unchanged. Thus, abnormal peripheral sprouting was unlikely to account for the increased mechanical sensitivity of the regenerated fibres. None of the regenerated nociceptors were found to be coupled to other fibres. 5. These results suggest that the clinical observation of mechanical hyperalgesia in patients after nerve injury may have a peripheral basis. Based on this model, other signs of neuropathic pain (i.e. tactile or thermal allodynia) are more likely to be due to altered central processing.