CD8+ and CD4+ T Cells Infiltrate into the Brain during Plasmodium berghei ANKA Infection and Form Long-Term Resident Memory

In the Plasmodium berghei ANKA mouse model of malaria, accumulation of CD8⁺ T cells and infected RBCs in the brain promotes the development of experimental cerebral malaria (ECM). In this study, we used malaria-specific transgenic CD4⁺ and CD8⁺ T cells to track evolution of T cell immunity during the acute and memory phases of P. berghei ANKA infection. Using a combination of techniques, including intravital multiphoton and confocal microscopy and flow cytometric analysis, we showed that, shortly before onset of ECM, both CD4⁺ and CD8⁺ T cell populations exit the spleen and begin infiltrating the brain blood vessels. Although dominated by CD8⁺ T cells, a proportion of both T cell subsets enter the brain parenchyma, where they are largely associated with blood vessels. Intravital imaging shows these cells moving freely within the brain parenchyma. Near the onset of ECM, leakage of RBCs into areas of the brain can be seen, implicating severe damage. If mice are cured before ECM onset, brain infiltration by T cells still occurs, but ECM is prevented, allowing development of long-term resident memory T cell populations within the brain. This study shows that infiltration of malaria-specific T cells into the brain parenchyma is associated with cerebral immunopathology and the formation of brain-resident memory T cells. The consequences of these resident memory populations is unclear but raises concerns about pathology upon secondary infection.

Adrenergic regulation of the vasculature impairs leukocyte interstitial migration and suppresses immune responses

The sympathetic nervous system (SNS) controls various physiological functions via the neurotransmitter noradrenaline. Activation of the SNS in response to psychological or physical stress is frequently associated with weakened immunity. Here, we investigated how adrenoceptor signaling influences leukocyte behavior. Intravital two-photon imaging after injection of noradrenaline revealed transient inhibition of CD8⁺ and CD4⁺ T cell locomotion in tissues. Expression of β-adrenergic receptor in hematopoietic cells was not required for NA-mediated inhibition of motility. Rather, chemogenetic activation of the SNS or treatment with adrenergic receptor agonists induced vasoconstriction and decreased local blood flow, resulting in abrupt hypoxia that triggered rapid calcium signaling in leukocytes and halted cell motility. Oxygen supplementation reversed these effects. Treatment with adrenergic receptor agonists impaired T cell responses induced in response to viral and parasitic infections, as well as anti-tumor responses. Thus, stimulation of the SNS impairs leukocyte mobility, providing a mechanistic understanding of the link between adrenergic receptors and compromised immunity.

The NK cell granule protein NKG7 regulates cytotoxic granule exocytosis and inflammation

Immune-modulating therapies have revolutionized the treatment of chronic diseases, particularly cancer. However, their success is restricted and there is a need to identify new therapeutic targets. Here, we show that natural killer cell granule protein 7 (NKG7) is a regulator of lymphocyte granule exocytosis and downstream inflammation in a broad range of diseases. NKG7 expressed by CD4+ and CD8+ T cells played key roles in promoting inflammation during visceral leishmaniasis and malaria-two important parasitic diseases. Additionally, NKG7 expressed by natural killer cells was critical for controlling cancer initiation, growth and metastasis. NKG7 function in natural killer and CD8+ T cells was linked with their ability to regulate the translocation of CD107a to the cell surface and kill cellular targets, while NKG7 also had a major impact on CD4+ T cell activation following infection. Thus, we report a novel therapeutic target expressed on a range of immune cells with functions in different immune responses.

The Role of NK Cells and Innate Lymphoid Cells in Brain Cancer

The brain is considered an immune privileged site due to the high selectivity of the blood-brain barrier which restricts the passage of molecules and cells into the brain parenchyma. Recent studies have highlighted active immunosurveillance mechanisms in the brain. Here we review emerging evidence for the contribution of innate lymphoid cells (ILCs) including natural killer (NK) cells to the immunosurveillance of brain cancers focusing on glioblastoma, one of the most aggressive and most common malignant primary brain tumors diagnosed in adults. Moreover, we discuss how the local tissue microenvironment and unique cellular interactions influence ILC functions in the brain and how these interactions might be successfully harnessed for cancer immunotherapy using insights gained from the studies of autoimmunity, aging, and CNS injury.

Cerebral Malaria in Mouse and Man

Cerebral malaria (CM) is an acute encephalopathy caused by the malaria parasite Plasmodium falciparum, which develops in a small minority of infected patients and is responsible for the majority of deaths in African children. Despite decades of research on CM, the pathogenic mechanisms are still relatively poorly defined. Nevertheless, many studies in recent years, using a combination of animal models, in vitro cell culture work, and human patients, provide significant insight into the pathologic mechanisms leading to CM. In this review, we summarize recent findings from mouse models and human studies on the pathogenesis of CM, understanding of which may enable development of novel therapeutic approaches.

Development of a Novel CD4+ TCR Transgenic Line That Reveals a Dominant Role for CD8+ Dendritic Cells and CD40 Signaling in the Generation of Helper and CTL Responses to Blood-Stage Malaria

We describe an MHC class II (I-A^b)-restricted TCR transgenic mouse line that produces CD4⁺ T cells specific for Plasmodium species. This line, termed PbT-II, was derived from a CD4⁺ T cell hybridoma generated to blood-stage Plasmodium berghei ANKA (PbA). PbT-II cells responded to all Plasmodium species and stages tested so far, including rodent (PbA, P. berghei NK65, Plasmodium chabaudi AS, and Plasmodium yoelii 17XNL) and human (Plasmodium falciparum) blood-stage parasites as well as irradiated PbA sporozoites. PbT-II cells can provide help for generation of Ab to P. chabaudi infection and can control this otherwise lethal infection in CD40L-deficient mice. PbT-II cells can also provide help for development of CD8⁺ T cell-mediated experimental cerebral malaria (ECM) during PbA infection. Using PbT-II CD4⁺ T cells and the previously described PbT-I CD8⁺ T cells, we determined the dendritic cell (DC) subsets responsible for immunity to PbA blood-stage infection. CD8⁺ DC (a subset of XCR1⁺ DC) were the major APC responsible for activation of both T cell subsets, although other DC also contributed to CD4⁺ T cell responses. Depletion of CD8⁺ DC at the beginning of infection prevented ECM development and impaired both Th1 and follicular Th cell responses; in contrast, late depletion did not affect ECM. This study describes a novel and versatile tool for examining CD4⁺ T cell immunity during malaria and provides evidence that CD4⁺ T cell help, acting via CD40L signaling, can promote immunity or pathology to blood-stage malaria largely through Ag presentation by CD8⁺ DC.

Forced expression of muscle specific kinase slows postsynaptic acetylcholine receptor loss in a mouse model of MuSK myasthenia gravis

We investigated the influence of postsynaptic tyrosine kinase signaling in a mouse model of muscle‐specific kinase (MuSK) myasthenia gravis (MG). Mice administered repeated daily injections of IgG from MuSK MG patients developed impaired neuromuscular transmission due to progressive loss of acetylcholine receptor (AChR) from the postsynaptic membrane of the neuromuscular junction. In this model, anti‐MuSK‐positive IgG caused a reduction in motor endplate immunolabeling for phosphorylated Src‐Y418 and AChR β‐subunit‐Y390 before any detectable loss of MuSK or AChR from the endplate. Adeno‐associated viral vector (rAAV) encoding MuSK fused to enhanced green fluorescent protein (MuSK‐EGFP) was injected into the tibialis anterior muscle to increase MuSK synthesis. When mice were subsequently challenged with 11 daily injections of IgG from MuSK MG patients, endplates expressing MuSK‐EGFP retained more MuSK and AChR than endplates of contralateral muscles administered empty vector. Recordings of compound muscle action potentials from myasthenic mice revealed less impairment of neuromuscular transmission in muscles that had been injected with rAAV‐MuSK‐EGFP than contralateral muscles (empty rAAV controls). In contrast to the effects of MuSK‐EGFP, forced expression of rapsyn‐EGFP provided no such protection to endplate AChR when mice were subsequently challenged with MuSK MG IgG. In summary, the immediate in vivo effect of MuSK autoantibodies was to suppress MuSK‐dependent tyrosine phosphorylation of proteins in the postsynaptic membrane, while increased MuSK synthesis protected endplates against AChR loss. These results support the hypothesis that reduced MuSK kinase signaling initiates the progressive disassembly of the postsynaptic membrane scaffold in this mouse model of MuSK MG.

The neuromuscular junction: measuring synapse size, fragmentation and changes in synaptic protein density using confocal fluorescence microscopy

The neuromuscular junction (NMJ) is the large, cholinergic relay synapse through which mammalian motor neurons control voluntary muscle contraction. Structural changes at the NMJ can result in neurotransmission failure, resulting in weakness, atrophy and even death of the muscle fiber. Many studies have investigated how genetic modifications or disease can alter the structure of the mouse NMJ. Unfortunately, it can be difficult to directly compare findings from these studies because they often employed different parameters and analytical methods. Three protocols are described here. The first uses maximum intensity projection confocal images to measure the area of acetylcholine receptor (AChR)-rich postsynaptic membrane domains at the endplate and the area of synaptic vesicle staining in the overlying presynaptic nerve terminal. The second protocol compares the relative intensities of immunostaining for synaptic proteins in the postsynaptic membrane. The third protocol uses Fluorescence Resonance Energy Transfer (FRET) to detect changes in the packing of postsynaptic AChRs at the endplate. The protocols have been developed and refined over a series of studies. Factors that influence the quality and consistency of results are discussed and normative data are provided for NMJs in healthy young adult mice.

Muscle-specific kinase (MuSK) autoantibodies suppress the MuSK pathway and ACh receptor retention at the mouse neuromuscular junction

Muscle-specific kinase (MuSK) autoantibodies from myasthenia gravis patients can block the activation of MuSK in vitro and/or reduce the postsynaptic localization of MuSK. Here we use a mouse model to examine the effects of MuSK autoantibodies upon some key components of the postsynaptic MuSK pathway and upon the regulation of junctional ACh receptor (AChR) numbers. Mice became weak after 14 daily injections of anti-MuSK-positive patient IgG. The intensity and area of AChR staining at the motor endplate was markedly reduced. Pulse-labelling of AChRs revealed an accelerated loss of pre-existing AChRs from postsynaptic AChR clusters without a compensatory increase in incorporation of (newly synthesized) replacement AChRs. Large, postsynaptic AChR clusters were replaced by a constellation of tiny AChR microaggregates. Puncta of AChR staining also appeared in the cytoplasm beneath the endplate. Endplate staining for MuSK, activated Src, rapsyn and AChR were all reduced in intensity. In the tibialis anterior muscle there was also evidence that phosphorylation of the AChR β-subunit-Y390 was reduced at endplates. In contrast, endplate staining for β-dystroglycan (through which rapsyn couples AChR to the synaptic basement membrane) remained intense. The results suggest that anti-MuSK IgG suppresses the endplate density of MuSK, thereby down-regulating MuSK signalling activity and the retention of junctional AChRs locally within the postsynaptic membrane scaffold.

Effects of the ß2-adrenoceptor agonist, albuterol, in a mouse model of anti-MuSK myasthenia gravis

The β2-adrenergic receptor agonist, albuterol, has been reported beneficial in treating several forms of congenital myasthenia. Here, for the first time, we examined the potential benefit of albuterol in a mouse model of anti-Muscle Specific Kinase (MuSK) myasthenia gravis. Mice received 15 daily injections of IgG from anti-MuSK positive patients, which resulted in whole-body weakness. At neuromuscular junctions in the tibialis anterior and diaphragm muscles the autoantibodies caused loss of postsynaptic acetylcholine receptors, and reduced the amplitudes of the endplate potential and spontaneous miniature endplate potential in the diaphragm muscle. Treatment with albuterol (8 mg/kg/day) during the two-week anti-MuSK injection series reduced the degree of weakness and weight loss, compared to vehicle-treated mice. However, the compound muscle action potential recorded from the gastrocnemius muscle displayed a decremental response in anti-MuSK-injected mice whether treated with albuterol or vehicle. Ongoing albuterol treatment did not increase endplate potential amplitudes compared to vehicle-treated mice nor did it prevent the loss of acetylcholine receptors from motor endplates. On the other hand, albuterol treatment significantly reduced the degree of fragmentation of endplate acetylcholine receptor clusters and increased the extent to which the remaining receptor clusters were covered by synaptophysin-stained nerve terminals. The results provide the first evidence that short-term albuterol treatment can ameliorate weakness in a robust mouse model of anti-MuSK myasthenia gravis. The results also demonstrate that it is possible for albuterol treatment to reduce whole-body weakness without necessarily reversing myasthenic impairment to the structure and function of the neuromuscular junction.

Sequence of age-associated changes to the mouse neuromuscular junction and the protective effects of voluntary exercise

Loss of connections between motor neurons and skeletal muscle fibers contribute to motor impairment in old age, but the sequence of age-associated changes that precede loss of the neuromuscular synapse remains uncertain. Here we determine changes in the size of neuromuscular synapses within the tibialis anterior muscle across the life span of C57BL/6J mice. Immunofluorescence, confocal microscopy and morphometry were used to measure the area occupied by nerve terminal synaptophysin staining and postsynaptic acetylcholine receptors at motor endplates of 2, 14, 19, 22, 25 and 28month old mice. The key findings were: 1) At middle age (14-months) endplate acetylcholine receptors occupied 238±11 µm² and nerve terminal synaptophysin 168±14 µm² (mean ± SEM). 2) Between 14-months and 19-months (onset of old age) the area occupied by postsynaptic acetylcholine receptors declined 30%. At many endplates the large acetylcholine receptor plaque became fragmented into multiple smaller acetylcholine receptor clusters. 3) Between 19- and 25-months, the fraction of endplate acetylcholine receptors covered by synaptophysin fell 21%. By 28-months, half of the endplates imaged retained ≤50 µm² area of synaptophysin staining. 4) Within aged muscles, the degree to which an endplate remained covered by synaptophysin did not depend upon the total area of acetylcholine receptors, nor upon the number of discrete receptor clusters. 5) Voluntary wheel-running exercise, beginning late in middle-age, prevented much of the age-associated loss of nerve terminal synaptophysin. In summary, a decline in the area of endplate acetylcholine receptor clusters at the onset of old age was followed by loss of nerve terminal synaptophysin from the endplate. Voluntary running exercise, begun late in middle age, substantially inhibited the loss of nerve terminal from aging motor endplates.

Pyridostigmine but not 3,4-diaminopyridine exacerbates ACh receptor loss and myasthenia induced in mice by muscle-specific kinase autoantibody

In myasthenia gravis, the neuromuscular junction is impaired by the antibody-mediated loss of postsynaptic acetylcholine receptors (AChRs). Muscle weakness can be improved upon treatment with pyridostigmine, a cholinesterase inhibitor, or with 3,4-diaminopyridine, which increases the release of ACh quanta. The clinical efficacy of pyridostigmine is in doubt for certain forms of myasthenia. Here we formally examined the effects of these compounds in the antibody-induced mouse model of anti-muscle-specific kinase (MuSK) myasthenia gravis. Mice received 14 daily injections of IgG from patients with anti-MuSK myasthenia gravis. This caused reductions in postsynaptic AChR densities and in endplate potential amplitudes. Systemic delivery of pyridostigmine at therapeutically relevant levels from days 7 to 14 exacerbated the anti-MuSK-induced structural alterations and functional impairment at motor endplates in the diaphragm muscle. No such effect of pyridostigmine was found in mice receiving control human IgG. Mice receiving smaller amounts of MuSK autoantibodies did not display overt weakness, but 9 days of pyridostigmine treatment precipitated generalised muscle weakness. In contrast, one week of treatment with 3,4-diaminopyridine enhanced neuromuscular transmission in the diaphragm muscle. Both pyridostigmine and 3,4-diaminopyridine increase ACh in the synaptic cleft yet only pyridostigmine potentiated the anti-MuSK-induced decline in endplate ACh receptor density. These results thus suggest that ongoing pyridostigmine treatment potentiates anti-MuSK-induced AChR loss by prolonging the activity of ACh in the synaptic cleft.

Muscle specific kinase: organiser of synaptic membrane domains

Muscle Specific Kinase (MuSK) is a transmembrane tyrosine kinase vital for forming and maintaining the mammalian neuromuscular junction (NMJ: the synapse between motor nerve and skeletal muscle). MuSK expression switches on during skeletal muscle differentiation. MuSK then becomes restricted to the postsynaptic membrane of the NMJ, where it functions to cluster acetylcholine receptors (AChRs). The expression, activation and turnover of MuSK are each regulated by signals from the motor nerve terminal. MuSK forms the core of an emerging signalling complex that can be acutely activated by neural agrin (N-agrin), a heparin sulfate proteoglycan secreted from the nerve terminal. MuSK activation initiates complex intracellular signalling events that coordinate the local synthesis and assembly of synaptic proteins. The importance of MuSK as a synapse organiser is highlighted by cases of autoimmune myasthenia gravis in which MuSK autoantibodies can deplete MuSK from the postsynaptic membrane, leading to complete disassembly of the adult NMJ.

Patient autoantibodies deplete postsynaptic muscle-specific kinase leading to disassembly of the ACh receptor scaffold and myasthenia gravis in mice

The postsynaptic muscle-specific kinase (MuSK) coordinates formation of the neuromuscular junction (NMJ) during embryonic development. Here we have studied the effects of MuSK autoantibodies upon the NMJ in adult mice. Daily injections of IgG from four MuSK autoantibody-positive myasthenia gravis patients (MuSK IgG; 45 mg day(1)i.p. for 14 days) caused reductions in postsynaptic ACh receptor (AChR) packing as assessed by fluorescence resonance energy transfer (FRET). IgG from the patients with the highest titres of MuSK autoantibodies caused large (51-73%) reductions in postsynaptic MuSK staining (cf. control mice; P < 0.01) and muscle weakness. Among mice injected for 14 days with control and MuSK patient IgGs, the residual level of MuSK correlated with the degree of impairment of postsynaptic AChR packing. However, the loss of postsynaptic MuSK preceded this impairment of postsynaptic AChR. When added to cultured C2 muscle cells the MuSK autoantibodies caused tyrosine phosphorylation of MuSK and the AChR beta-subunit, and internalization of MuSK from the plasma membrane. The results suggest a pathogenic mechanism in which MuSK autoantibodies rapidly deplete MuSK from the postsynaptic membrane leading to progressive dispersal of postsynaptic AChRs. Moreover, maintenance of postsynaptic AChR packing at the adult NMJ would appear to depend upon physical engagement of MuSK with the AChR scaffold, notwithstanding activation of the MuSK-rapsyn system of AChR clustering.

Levels of naturally occurring microorganisms on surgical instruments after clinical use and after washing

Surgical instruments exposed to sterile body sites should be contaminated with relatively low levels of microbial contamination or bioburden; however, few studies in the literature have determined the quantitative level and types of contamination. A study was conducted at 2 clinical sites to determine the level of microbial contamination of surgical instruments after clinical use and after washing. Quantitative assays showed that bioburden levels were in the range of 0 to 4415 colony forming units per instrument after clinical use, and 88% of the instruments had bioburden levels lower than 1000. As expected, a reduction in counts occurred after washing; however, in some cases, higher counts were found on the instruments after the washing process. Although the washing procedure is effective in reducing the microbial levels deposited on the surgical instruments during use, a recontamination process occurs that results in increased counts after washing. The low bioburden level after washing consists of predominantly vegetative microorganisms that present a relatively low challenge to sterilization and disinfection systems.

Shivering and shivering-like tremor during labor with and without epidural analgesia

BACKGROUND

Effective treatment and prevention of hyperthermia and shivering-like tremor during labor is hindered by a poor understanding of their causes. The authors sought to identify the incidence of nonthermoregulatory shivering-like tremor and the factors associated with this activity.

METHODS

The authors studied women in spontaneous full-term labor who chose epidural analgesia (n = 21) or opioid sedation (n = 31). Shivering-like tremor and sweating were evaluated by observation. Core temperature was recorded in the external auditory canal using a compensated infrared thermometer. Arteriovenous shunt tone was evaluated with forearm minus fingertip skin temperature gradients; gradients less than 0 were considered evidence of vasodilation. Tremor was considered nonthermoregulatory when core temperature exceeded 37 degrees C and the arms were vasodilated. Pain was evaluated using a visual analog scale.

RESULTS

Shivering-like tremor was observed in 18% of 290, 30-min data-acquisition epochs before delivery. The patients were both normothermic and vasodilated during 15% of these epochs. Shivering was observed in 16% of 116 postdelivery epochs and was nonthermoregulatory in 28%. Sweating was observed in 30% of predelivery epochs, and the patients were both hypothermic and vasoconstricted during 12%. The mean core temperature in patients given epidural analgesia was approximately 0.2 degrees C greater than in those given sedation. Hyperthermia was observed during 10 epochs (38.4+/-0.3 degrees C) during epidural analgesia and during 10 epochs (38.4+/-0.3 degrees C) with sedation. The patients were vasoconstricted in more than 50% of these epochs in each group. Multivariate mixed-effects modeling identified high pain scores and vasoconstriction as significant predictors of shivering. There were no predictors for shivering epochs in patients who were simultaneously normothermic and vasodilated. Significant predictors of sweating were time before delivery, high pain scores, hypothermia with vasoconstriction, high thermal comfort, and low mean skin temperature. There were no predictors for sweating epochs in patients who were simultaneously hypothermic and vasoconstricted.

CONCLUSIONS

This study confirms the clinical impression that some peripartum shivering-like tremor is nonthermoregulatory. The authors also identified nonthermoregulatory sweating. These data indicate that shivering-like tremor and sweating in the peripartum period is multifactorial.