T-cell activation, proliferation and apoptosis in primary Listeria monocytogenes infection

Listeria monocytogenes infection of mice leads to a rapid expansion of activated T cells, followed by a decline in specific cells once the bacteria are eliminated. In order to define the relationship between T-cell proliferation and activation, and to investigate the role of apoptosis in limiting the expansion, the expression of activation markers, uptake of 5-bromo-2'-deoxyuridine (BrdU) in vivo and the incidence of apoptosis was investigated. Increased numbers of T cells expressing the activated phenotype CD25+, CD44hi and CD62Llo were detected 4 days after infection. Expression of CD25 (IL-2Ralpha chain) on CD4+ and CD8+ T cells peaked at this time and returned to normal by day 7. In contrast, CD44hi and CD62Llo persisted, with the maximum proportion occurring at 7 days after infection. This was accompanied by a burst of in vivo proliferation of CD4+ and CD8+ T cells occurring between day 5 and 7. Apoptosis, which is presumably needed to control this expansion of T cells, also peaked at 7 days after infection. Apoptosis occurred preferentially amongst T cells which had proliferated. Most but not all proliferating T cells had down-regulated their CD62L marker. While most apoptotic T cells were CD62Llo, again not all had down-regulated this marker. Hence, CD25 expression peaked early, but expression of other activation markers, in vivo proliferation and apoptosis coincided after Listeria infection. T cells that had proliferated were over-represented in the apoptotic population.     

Microglial activation in healthy aging

Healthy brain aging is characterized by neuronal loss and decline of cognitive function. Neuronal loss is closely associated with microglial activation and postmortem studies have indeed suggested that activated microglia may be present in the aging brain. Microglial activation can be quantified in vivo using (R)-[(11)C]PK11195 and positron emission tomography. The purpose of this study was to measure specific binding of (R)-[(11)C]PK11195 in healthy subjects over a wide age range. Thirty-five healthy subjects (age range 19-79 years) were included. In all subjects 60-minute dynamic (R)-[(11)C]PK11195 scans were acquired. Specific binding of (R)-[(11)C]PK11195 was calculated using receptor parametric mapping in combination with supervised cluster analysis to extract the reference tissue input function. Increased binding of (R)-[(11)C]PK11195 with aging was found in frontal lobe, anterior and posterior cingulate cortex, medial inferior temporal lobe, insula, hippocampus, entorhinal cortex, thalamus, parietal and occipital lobes, and cerebellum. This indicates that activated microglia appear in several cortical and subcortical areas during healthy aging, suggesting widespread neuronal loss.     

PKC-beta controls I kappa B kinase lipid raft recruitment and activation in response to BCR signaling

NF-kappa B signaling is required for the maintenance of normal B lymphocytes, whereas dysregulated NF-kappa B activation contributes to B cell lymphomas. The events that regulate NF-kappa B signaling in B lymphocytes are poorly defined. Here, we demonstrate that PKC-beta is specifically required for B cell receptor (BCR)-mediated NF-kappa B activation. B cells from protein kinase C-beta (PKC-beta)-deficient mice failed to recruit the I kappa B kinase (IKK) complex into lipid rafts, activate IKK, degrade I kappa B or up-regulate NF-kappa B-dependent survival signals. Inhibition of PKC-beta promoted cell death in B lymphomas characterized by exaggerated NF-kappa B activity. Together, these data define an essential role for PKC-beta in BCR survival signaling and highlight PKC-beta as a key therapeutic target for B-lineage malignancies.     

Microglial response to amyloid plaques in APPsw transgenic mice.

Microglial activation is central to the inflammatory response in Alzheimer's Disease (AD). A recently described mouse line, Tg(HuAPP695.K670N/M671L)2576, expressing human amyloid precursor protein with a familial AD gene mutation, age-related amyloid deposits, and memory deficits, was found to develop a significant microglial response using Griffonia simplicifolia lectin or phosphotyrosine probe to identify microglia Both Griffonia simplicifolia lectin and phosphotyrosine staining showed increased numbers of intensely labeled, often enlarged microglia clustered in and around plaques, consistent with microglial activation related to beta-amyloid formation. Using quantitative image analysis of coronal phosphotyrosine-immunostained sections, transgene-positive 10- to 16-month-old, hemizygous, hybrid Tg2576 (APPsw) animals showed significantly increased microglial density and size in plaque-forming areas of hippocampus and frontal, entorhinal, and occipital cortex. Quantitative analysis of microglia as a function of distance from the center of plaques (double labeled for A beta peptide and microglia) revealed highly significant, two- to fivefold elevations in microglial number and area within plaques compared with neighboring regions. Tg2576 beta-amyloid-plaque-forming mice should be a useful system for assessing the consequences of the microglial-mediated inflammatory response to beta-amyloid and developing anti-inflammatory therapeutic strategies for Alzheimer's disease. These results provide the first quantitative link between beta-amyloid plaque formation and microglial activation in an animal model with neuritic plaques and memory deficits.     

Microglial response to brain injury: a brief synopsis

In addition to astrocytes and oligodendrocytes, microglia represent the third major population of glial cells within the central nervous system (CNS). Microglia are distributed ubiquitously throughout the brain and spinal cord, and one of their main functions is to monitor and sustain neuronal health. Microglial cells are quite sensitive to even minor disturbances in CNS homeostasis, and they become readily activated during most neuropathologic conditions, including peripheral nerve injury, trauma and stroke, inflammatory disease, and neurotoxicant-induced neuronal injury. During activation, microglia display conspicuous functional plasticity, which involves changes in cell morphology, cell number, cell surface receptor expression, and production of growth factors and cytokines. The many changes occurring in activated cells reflect the altered functional states of microglia that are induced by signals arising from injured neurons. Thus, neuronal-microglial signaling plays a fundamental role in understanding how the CNS responds to injury. Reactive microgliosis should be viewed as a cellular effort to initiate ameliorative and reparative measures in the injured brain.     

Microglial activation in the developing rat olfactory bulb

The development of the olfactory bulb, the primary central relay of the olfactory system, is characterized by a striking susceptibility to alterations in the amount of afferent input. For example, blocking airflow through one half of the nasal cavity during early life results in a number of dramatic changes in the bulb, including increased cell death. Previous studies reveal high levels of microglia in the olfactory bulb. Microglia function as phagocytes, aid in synaptogenesis, and produce important trophic and cytotoxic factors. In response to a number of tissue perturbations, microglia undergo an activation process that includes, among other changes, the up-regulation of complement receptor 3. Interestingly, a previous study reported that naris closure had no effect on microglia in the bulb; however, the research did not distinguish the functional activation state of microglia. We further examined the role of microglia in the normally developing and olfactory-deprived rat bulb using immunohistochemical detection of complement receptor 3 as a measure of microglial activation. Expression of the receptor in the bulb is relatively high during postnatal development, in particular when compared to levels in cortical regions caudal to the olfactory bulb. In addition, naris closure performed on the day after birth (but not after the first postnatal month) increases levels of the receptor in an age and laminar-dependent fashion.The presence of an inducible pool of activated microglia in the olfactory bulb may be important for normal development and contribute to the plethora of changes seen after early olfactory deprivation.     

Human telomerase: biogenesis,trafficking, recruitment,and activation

Telomerase is the ribonucleoprotein enzyme that catalyzes the extension of telomeric DNA in eukaryotes. Recent work has begun to reveal key aspects of the assembly of the human telomerase complex, its intracellular trafficking involving Cajal bodies, and its recruitment to telomeres. Once telomerase has been recruited to the telomere, it appears to undergo a separate activation step, which may include an increase in its repeat addition processivity. This review covers human telomerase biogenesis, trafficking, and activation, comparing key aspects with the analogous events in other species.     

Microglial activation and neuronal apoptosis in Bornavirus infected neonatal Lewis rats

Lewis rats neonatally infected with Borna disease virus have a behavioral syndrome characterized by hyperactivity, movement disorders, and abnormal social interactions. Virus is widely distributed in brain; however, neuropathology is focused in dentate gyrus, cerebellum, and neocortex where granule cells, Purkinje cells and pyramidal cells are lost through apoptosis. Although a transient immune response is present, its distribution does not correlate with sites of damage. Neuropathology is instead colocalized with microglial proliferation and expression of MHC class I and class II, ICAM, CD4 and CD8 molecules. Targeted pathogenesis in this system appears to be linked to microglial activation and susceptibility of specific neuronal populations to apoptosis rather than viral tropism or virus-specific immune responses.     

Microglial MHC class II is dispensable for experimental autoimmune encephalomyelitis and cuprizone‐induced demyelination

Microglia are resident immune cells in the CNS, strategically positioned to clear dead cells and debris, and orchestrate CNS inflammation and immune defense. In steady state, these macrophages lack MHC class II (MHCII) expression, but microglia activation can be associated with MHCII induction. Whether microglial MHCII serves antigen presentation for critical local T‐cell restimulation in CNS auto‐immune disorders or modulates microglial signaling output remains under debate. To probe for such scenarios, we generated mice harboring an MHCII deficiency in microglia, but not peripheral myeloid cells. Using the CX₃CR1^CreER‐based approach we report that microglial antigen presentation is obsolete for the establishment of EAE, with disease onset, progression, and severity unaltered in mutant mice. Antigen presentation‐independent roles of microglial MHCII were explored using a demyelination model induced by the copper chelator cuprizone. Absence of microglial I‐A^b did not affect the extent of these chemically induced white matter alterations, nor did it affect microglial proliferation or gene expression associated with locally restricted de‐ and remyelination.     

Lymphocyte recruitment and homing to the liver in primary biliary cirrhosis and primary sclerosing cholangitis

The mechanisms operating in lymphocyte recruitment and homing to liver are reviewed. A literature review was performed on primary biliary cirrhosis (PBC), progressive sclerosing cholangitis (PSC), and homing mechanisms; a total of 130 papers were selected for discussion. Available data suggest that in addition to a specific role for CCL25 in PSC, the CC chemokines CCL21 and CCL28 and the CXC chemokines CXCL9 and CXCL10 are involved in the recruitment of T lymphocytes into the portal tract in PBC and PSC. Once entering the liver, lymphocytes localize to bile duct and retain by the combinatorial or sequential action of CXCL12, CXCL16, CX3CL1, and CCL28 and possibly CXCL9 and CXCL10. The relative importance of these chemokines in the recruitment or the retention of lymphocytes around the bile ducts remains unclear. The available data remain limited but underscore the importance of recruitment and homing.     

Reversible demyelination, blood-brain barrier breakdown, and pronounced neutrophil recruitment induced by chronic IL-1 expression in the brain

Interleukin-1beta (IL-1) expression is associated with a spectrum of neuroinflammatory processes related to chronic neurodegenerative diseases. The single-bolus microinjection of IL-1 into the central nervous system (CNS) parenchyma gives rise to delayed and localized neutrophil recruitment, transient blood-brain barrier (BBB) breakdown, but no overt damage to CNS integrity. However, acute microinjections of IL-1 do not mimic the chronic IL-1 expression, which is a feature of many CNS diseases. To investigate the response of the CNS to chronic IL-1 expression, we injected a recombinant adenovirus expressing IL-1 into the striatum. At the peak of IL-1 expression (days 8 and 14 post-injection), there was a marked recruitment of neutrophils, vasodilatation, and breakdown of the BBB. Microglia and astrocyte activation was evident during the first 14 days post-injection. At days 8 and 14, extensive demyelination was observed but the number of neurons was not affected by any treatment. Finally, at 30 days, signs of inflammation were no longer present, there was evidence of tissue reorganization, the BBB was intact, and the process of remyelination was noticeable. In summary, our data show that chronic expression of IL-1, in contrast to its acute delivery, can reversibly damage CNS integrity and implicates this cytokine or downstream components as major mediators of demyelination in chronic inflammatory and demyelinating diseases.     

Lymphocyte proliferation in response to exercise

Lymphocyte proliferative responses are often used to evaluate the functional capacity of the immune system in response to exercise. Blood mononuclear cells (BMNC) are stimulated in vitro with polyclonal mitogens and the incorporation of ³H-thymidine into the DNA reflects cell proliferation. The BMNC are most often stimulated with either phytohaemagglutinin (PHA), poke weed mitogen (PWM), concanavalin A (Con-A), interleukin-2 (IL-2), or purified derivative of tuberculin (PPD). The literature concerning lymphocyte proliferation and exercise is reviewed with respect to the type and intensity of exercise, and also the effect of training status. The proliferative responses to exercise are highly heterogeneous, the most consistent finding being that PHA-stimulated cell responses decrease during exercise which may reflect a decreased fraction of CD3+ cells. In contrast, reduced, elevated or even unchanged lymphocyte proliferative response to PHA, PWM, Con-A, IL-2 and PPD have been demonstrated in the recovery period following exercise. Also variable responses are present in trained athletes compared to less fit subjects. Even though this may reflect that the time of ³H-thymidine incorporation into lymphocytes varies, we conclude that a functional evaluation of the immune system in response to exercise cannot be based solely upon measurements of lymphocyte proliferation.     

Induction of oligodendrocyte proliferation and remyelination after chronic demyelination. Relevance to multiple sclerosis

Optic nerve and spinal cord tissue from untreated guinea pigs with chronic relapsing experimental autoimmune encephalomyelitis, guinea pigs with experimental autoimmune encephalomyelitis in which the disease was treated with injections of myelin basic protein (MBP) combined with galactocerebroside (GC), and normal guinea pigs, has been studied morphologically, immunocytochemically and morphometrically. MBP/GC treatment induced widespread proliferation of oligodendrocytes and extensive central nervous system (CNS) remyelination in tissue from both sites. Whereas some oligodendrocytes within lesions from treated animals appeared to be derived from surviving cells which underwent mitosis, the frequent occurrence of nests of oligodendrocytes at the periphery of nerve fiber fascicles in optic nerve among perivascular astrocytic elements, raises the possibility that remyelinating oligodendrocytes might possess progenitors located in these regions. Observations from multiple sclerosis lesions showed that oligodendrocyte proliferation and CNS remyelination occur in human subcortical white matter, but to a lesser degree than that seen in the CNS of MBP/GC/treated guinea pigs. Immunocytochemical examination of CNS tissue from experimental autoimmune encephalomyelitis animals confirmed the morphologic identification of oligodendroglia. Preliminary morphometric analysis confirmed the impression of an increase in oligodendroglial cells in MBP/GC-treated animals. This increase was somewhat obscured statistically by a concomitant rise in the number of fibrous astrocytes. In view of the ability of oligodendrocytes to proliferate and produce new myelin in multiple sclerosis, the possibility is raised that an experimental immunologic approach similar to that employed here might have a beneficial effect in the human disease.     

Autonomous induction of proliferation, JNK and NF-alphaB activation in primary resting T cells by mobilized CD28

Induction of proliferation in primary resting T cells requires engagement of both the antigen-specific TCR and the co-stimulatory receptor CD28. Here we report that CD28 functions as an autonomous mitogenic receptor which is mobilized by TCR signaling through cytoskeletal rearrangement. Shortcutting of TCR-dependent CD28 recruitment by stimulation with monoclonal antibodies specific for mobilized CD28 results in maximum proliferation and IL-2 secretion in primary resting T cells without activation of ZAP-70, a central component of the TCR's signal transduction machinery. Engagement of mobilized CD28 fully activates the c-Jun N-terminal kinase cascade and translocation of NF-alphaB, two key targets of signal integration in co-stimulation. We propose a two-step activation model for co-stimulation in primary resting T cells in which antigen recognition recruits co-stimulatory receptors which then autonomously transduce signals promoting T cell proliferation.     

The response of NG2-expressing oligodendrocyte progenitors to demyelination in MOG-EAE and MS

Remyelination of primary demyelinated lesions is a common feature of experimental models of multiple sclerosis (MS) and is also suggested to be the normal response to demyelination during the early stages of MS itself. Many lines of evidence have shown that remyelination is preceded by the division of endogenous oligodendrocyte precursor cells (OPCs) in the lesion and its borders. It is suggested that this rapid response of OPCs to repopulate the lesion site and their subsequent differentiation into new oligodendrocytes is the key to the rapid remyelination. Antibodies to the NG2 chondroitin sulphate proteoglycan have proved exceedingly useful in following and quantitating the response of endogenous OPCs to demyelination. Here we review the literature on the response of NG2-expressing OPCs to demyelination and provide some new evidence on their response to the chronic inflammatory demyelinating environment seen in recombinant myelin oligodendrocyte glycoprotein (MOG) induced experimental allergic encephalomyelitis (EAE) in the DA rat. NG2-expressing OPCs responded to the inflammatory demyelination in this model by becoming reactive and increasing in number in a very focal manner. Evidence of NG2⁺OPCs in lesioned areas beginning to express the oligodendrocyte marker CNP was also seen. The response of OPCs appeared to occur following successive relapses but did not always lead to remyelination, with areas of chronic demyelination observed in the spinal cord. The presence of OPCs in the adult human CNS is clearly of vital importance for repair in multiple sclerosis (MS). As in rat tissue, the antibody labels an evenly distributed cell population present in both white and grey matter, distinct from HLA-DR⁺microglia. NG2⁺cells are sparsely distributed in the centre of chronic MS lesions. These cells apparently survive demyelination and exhibit a multi-processed or bipolar morphology in the very hypocellular environment of the lesion.     

Comparative study of proliferation of suckling and adult rat hepatocytes in primary culture in response to growth-stimulating factors

The replicative responses of suckling and adult rat hepatocytes in primary culture to growth-stimulating factors were compared. By addition of L-proline alone, the [3H]-thymidine labeling of suckling rat hepatocytes was dramatically enhanced, but that of adult ones was not. Epidermal growth factor (EGF), insulin, triiodothyronine (T3) and glucagon also enhanced the labeling of suckling rat hepatocytes regardless of the presence or the absence of L-proline. On the other hand, in the absence of L-proline, only EGF enhanced the labeling of adult rat hepatocytes, and, in the presence of L-proline, insulin as well as EGF enhanced the labeling. In the presence of growth factors and L-proline, the number of suckling rat hepatocytes increased up to about 143%, whereas that of adult rat hepatocytes hardly increased. Thus, a remarkable difference in replicative responses to growth factors and L-proline was observed between suckling and adult rat hepatocytes in primary culture.     

Motor unit recruitment in human genioglossus muscle in response to hypercapnia

Study Objectives:

Single motor unit recordings of the genioglossus (GG) muscle indicate that GG motor units have a variety of discharge patterns, including units that have higher discharge rates during inspiration (inspiratory phasic and inspiratory tonic), or expiration (expiratory phasic and expiratory tonic), or do not modify their rate with respiration (tonic). Previous studies have shown that an increase in GG muscle activity is a consequence of increased activity in inspiratory units. However, there are differences between studies as to whether this increase is primarily due to recruitment of new motor units (motor unit recruitment) or to increased discharge rate of already active units (rate coding). Sleep-wake state studies in humans have suggested the former, while hypercapnia experiments in rats have suggested the latter. In this study, we investigated the effect of hypercapnia on GG motor unit activity in humans during wakefulness.

Setting:

Sleep research laboratory.

Participants:

Sixteen healthy men.

Measurements and Results:

Each participant was administered at least 6 trials with P_etCO₂ being elevated 8.4 (SD = 1.96) mm Hg over 2 min following a 30-s baseline. Subjects were instrumented for GG EMG and respiratory measurements with 4 fine wire electrodes inserted subcutaneously into the muscle. One hundred forty-one motor units were identified during the baseline: 47% were inspiratory modulated, 29% expiratory modulated, and 24% showed no respiratory related modulation. Sixty-two new units were recruited during hypercapnia. The distribution of recruited units was significantly different from the baseline distribution, with 84% being inspiratory modulated (P < 0.001). Neither units active during baseline, nor new units recruited during hypercapnia, increased their discharge rate as P_etCO₂ increased (P > 0.05 for all comparisons).

Conclusions:

Increased GG muscle activity in humans occurs because of recruitment of previously inactive inspiratory modulated units.

Citation:

Nicholas CL; Bei B; Worsnop C; Malhotra A; Jordan AS; Saboisky JP; Chan JKM; Duckworth E; White DP; Trinder J. Motor unit recruitment in human genioglossus muscle in response to hypercapnia. SLEEP 2010;33(11):1529-1538.