In vivo model to study the impact of genetic variation on clinical outcome of mastitis in uniparous dairy cows.

BACKGROUND: In dairy herds, mastitis causes detrimental economic losses. Genetic selection offers a sustainable tool to select animals with reduced susceptibility towards postpartum diseases. Studying underlying mechanisms is important to assess the physiological processes that cause differences between selected haplotypes. Therefore, the objective of this study was to establish an in vivo infection model to study the impact of selecting for alternative paternal haplotypes in a particular genomic region on cattle chromosome 18 for mastitis susceptibility under defined conditions in uniparous dairy cows. RESULTS: At the start of pathogen challenge, no significant differences between the favorable (Q) and unfavorable (q) haplotypes were detected. Intramammary infection (IMI) with Staphylococcus aureus 1027 (S. aureus, n = 24, 96 h) or Escherichia coli 1303 (E. coli, n = 12, 24 h) was successfully induced in all uniparous cows. This finding was confirmed by clinical signs of mastitis and repeated recovery of the respective pathogen from milk samples of challenged quarters in each animal. After S. aureus challenge, Q-uniparous cows showed lower somatic cell counts 24 h and 36 h after challenge (P < 0.05), lower bacterial shedding in milk 12 h after challenge (P < 0.01) and a minor decrease in total milk yield 12 h and 24 h after challenge (P < 0.01) compared to q-uniparous cows. CONCLUSION: An in vivo infection model to study the impact of genetic selection for mastitis susceptibility under defined conditions in uniparous dairy cows was successfully established and revealed significant differences between the two genetically selected haplotype groups. This result might explain their differences in susceptibility towards IMI. These clinical findings form the basis for further in-depth molecular analysis to clarify the underlying genetic mechanisms for mastitis resistance.

Genetic selection for bovine chromosome 18 haplotypes associated with divergent somatic cell score affects postpartum reproductive and metabolic performance.

The susceptibility of animals to periparturient diseases has a great effect on the economic efficiency of dairy industries, on the frequency of antibiotic treatment, and on animal welfare. The use of selection for breeding cows with reduced susceptibility to diseases offers a sustainable tool to improve dairy cattle farming. Several studies have focused on the association of distinct bovine chromosome 18 genotypes or haplotypes with performance traits. The aim of this study was to test whether selection of Holstein Friesian heifers via SNP genotyping for alternative paternal chromosome 18 haplotypes associated with favorable (Q) or unfavorable (q) somatic cell scores influences postpartum reproductive and metabolic diseases. Thirty-six heifers (18 Q and 18 q) were monitored from 3 wk before calving until necropsy on d 39 (± 4 d) after calving. Health status and rectal temperature were measured daily, and body condition score and body weight were assessed once per week. Blood samples were drawn twice weekly, and levels of insulin, nonesterified fatty acids, insulin-like growth factor-I, growth hormone, and ß-hydroxybutyrate were measured. Comparisons between the groups were performed using Fisher's exact test, chi-squared test, and the GLIMMIX procedure in SAS. Results showed that Q-heifers had reduced incidence of metritis compared with q-heifers and were less likely to develop fever. Serum concentrations of ß-hydroxybutyrate were lower and insulin-like growth factor-I plasma concentrations were higher in Q- compared with q-heifers. However, the body condition score and withers height were comparable between haplotypes, but weight loss tended to be lower in Q-heifers compared with q-heifers. No differences between the groups were detected concerning retained fetal membranes, uterine involution, or onset of cyclicity. In conclusion, selection of chromosome 18 haplotypes associated with a reduced somatic cell score resulted in a decreased incidence of postpartum reproductive and metabolic diseases in this study. The presented data add to the existing knowledge aimed at avoiding negative consequences of genetic selection strategies in dairy cattle farming. The underlying causal mechanisms modulated by haplotypes in the targeted genomic region and immune competence necessitate further investigation.

The role of microglia and macrophages in the pathophysiology of the CNS.

Microglia are a major ghal component of the central nervous system (CNS) and are extremely sessile. Only a subtype, the perivascular microglia, are regularly replaced from the bone marrow in adult animals. Microglia respond to virtually any, even minor pathological events in the CNS. In most pathological settings microglia are aided by infiltrating hematogenous macrophages. Upon activation microglia and macrophages share most phenotypical markers and can exert similar effector functions. After transection of a CNS fibre tract microglia are insufficiently activated and hematogenous macrophages do not significantly enter the degenerating nerve stump. Thereby myelin debris that contains neurite outgrowth inhibiting activity persists for long time. This is in sharp contrast to the peripheral nervous system in which hematogenous macrophages are rapidly recruited in response to axotomy and clear myelin debris allowing regrowth of axons from the proximal stump. However, CNS lesion paradigms with breakdown of the blood-brain barrier such as cerebral ischemia, brain abscesses and stab wounds elicit prompt microglial activation, macrophage recruitment and debris clearance. There is increasing evidence that microglia play an active part in degenerative CNS diseases. In Alzheimer's disease activated microglia appear to be involved in plaque formation. In experimental globoid cell dystrophy T-cell independent induction of major histocompatibility complex class II molecules on microglia accelerates demyelination. In autoimmune diseases microglia probably have dual functions. Microglia present antigen to infiltrating T cells and exert effector functions thereby locally augmenting immune responses. On the other hand, microglia have the capacity to downregulate T cell responses. In the human acquired immunodeficiency syndrome (AIDS) virus infected macrophages probably introduce the virus to the CNS and in concert with microglia are involved in the pathophysiology of the AIDS dementia complex.

Inflammation and glial responses in ischemic brain lesions.

Focal cerebral ischemia elicits a strong inflammatory response involving early recruitment of granulocytes and delayed infiltration of ischemic areas and the boundary zones by T cells and macrophages. Infiltration of hematogenous leukocytes is facilitated by an upregulation of the cellular adhesion molecules P-selectin, intercellular adhesion molecule-1 and vascular adhesion molecule-1 on endothelial cells. Blocking of the leukocyte/endothelial cell adhesion process significantly reduces stroke volume after transient, but not permanent middle cerebral artery occlusion. In the infarct region microglia are activated within hours and within days transform into phagocytes. Astrocytes upregulate intermediate filaments, synthesize neurotrophins and form glial scars. Local microglia and infiltrating macrophages demarcate infarcts and rapidly remove debris. Remote from the lesion no cellular infiltration occurs, but astroglia and microglia are transiently activated. Astrocytic activation is induced by spreading depression. In focal ischemia neurons die acutely by necrosis and in a delayed fashion by programmed cell death, apoptosis. Proinflammatory cytokines such as tumor necrosis factor-alpha and interleukin-1 beta are upregulated within hours in ischemic brain lesions. Either directly or via induction of neurotoxic mediators such as nitric oxide, cytokines may contribute to infarct progression in the post-ischemic period. On the other hand, inflammation is tightly linked with rapid removal of debris and repair processes. At present it is unclear whether detrimental effects of inflammation outweigh neuroprotective mechanisms or vice versa. In global ischemia inflammatory responses are limited, but micro- and astroglia are also strongly activated. Glial responses significantly differ between brain regions with selective neuronal death and neighbouring areas that are more resistent to ischemic damage.

Chlamydia pneumoniae, herpes simplex virus and cytomegalovirus in symptomatic and asymptomatic high-grade internal carotid artery stenosis. Does infection influence plaque stability?

BACKGROUND: Current debates are focused on inflammatory processes in atherosclerotic lesions as a possible pathomechanism for destabilization and thrombembolism. In this prospective study the role of systemic and local infection in patients with high-grade internal carotid artery stenosis (ICA) was evaluated. PATIENTS AND METHODS: Serum antibody titers of 109 consecutive patients, who underwent surgery for ICA stenosis (asymptomatic n = 40, symptomatic n = 69) were prospectively measured for Chlamydia pneumoniae (Cpn) (IgA and IgG), Herpes simplex virus (HSV) (IgG, IgM) and Cytomegalovirus (CMV) (IgG, IgM) respectively. 53 carotis plaques of this group (asymptomatic n = 17, symptomatic n = 36) could be analyzed by polymerase chain reaction (PCR) for Cpn-, HSV- and CMV-DNA presence. RESULTS: Seropositivity was found in 61,5% for Cpn, 91,7% for HSV and 72,5% CMV respectively. No significant relation was found between symptomatic and asymptomatic patients as well as no difference was seen for presence of IgA antibodies against Cpn comparing both groups. Plaque-PCR revealed Cpn in 7 cases (13,2%), HSV in 2 cases (3,8%) and no CMV had been detected. Again, no significant relationship was found concerning symptomatic and asymptomatic patients. All 9 PCR-positive plaques displayed lesions of "complicated atherosclerosis" as central fibrous necrosis and calcification or plaque bleeding and surface thrombosis. CONCLUSIONS: Our results do not support the hypothesis that systemic Cpn, HSV or CMV- infection or evidence of Cpn-, HSV- or CMV-DNA in carotid plaques causes plaque destabilization and cerebral thromboembolism. Plaque infection could only be observed in cases with advanced atherosclerosis.

Differential recruitment of CD8+ macrophages during Wallerian degeneration in the peripheral and central nervous system.

The strong macrophage response occurring during Wallerian degeneration in the peripheral but not central nervous system has been implicated in tissue remodeling and growth factor production as key requirements for successful axonal regeneration. We have previously identified a population of CD8+ phagocytes in ischemic brain lesions that differed in its recruitment pattern from CD4+ macrophages/microglia found in other lesion paradigms. In the present study we show that crush injury to the sciatic nerve induced strong infiltration by CD8+ macrophages both at the crush site and into the degenerating distal nerve stump. At the crush site, CD8+ macrophages appeared within 24 hours whereas infiltration of the distal nerve parenchyma was delayed to the second week. CD8+ macrophages were ED1+ and CD11b+ but always MHC class II-. Most CD8+ macrophages coexpressed CD4 while a significant number of CD4+/CD8-macrophages was also present. Expression of the resident tissue macrophage marker ED2 was largely restricted to the CD4+/CD8- population. Following intraorbital crush injury to the optic nerve, infiltration of CD8+ macrophages was strictly confined to the crush site. Taken together, our study demonstrates considerable spatiotemporal diversity of CD8+ macrophage responses to axotomy in the peripheral and central nervous system that may have implications for the different extent of axonal regeneration observed in both systems.

Expression of tissue factor in high-grade carotid artery stenosis: association with plaque destabilization.

BACKGROUND AND PURPOSE: The procoagulant protein tissue factor (TF) has been implicated in thromboembolic complications associated with advanced atherosclerosis. In this study, we investigated whether TF expression in high-grade stenoses of the internal carotid artery (ICA) is associated with clinical features of plaque destabilization and addressed the relationship between TF expression and plaque inflammation. METHODS: In 36 consecutive patients undergoing surgery for high-grade ICA stenosis, clinical evidence of plaque instability was provided by the recent occurrence of ischemic symptoms attributable to the stenosis and the detection of cerebral microembolism by means of transcranial Doppler ultrasound monitoring of the ipsilateral middle cerebral artery. Endarterectomy specimens were stained immunocytochemically for TF expression as well as macrophage (CD68) and T cell (CD3) infiltration. RESULTS: Morphologically, TF immunoreactivity was codistributed with plaque inflammation and predominantly localized to CD68+ macrophages. Accordingly, statistical analysis revealed a significant association of TF expression with plaque infiltration by macrophages (P<0.0001) and T cells (P=0.013). Plaques extensively stained for TF (median of TF+ total section area >40% in semiquantitative assessment) were more frequent in symptomatic (12/27) than in asymptomatic patients (1/9). Conversely, plaques exhibiting little TF expression (median of TF+ section area <20%) were more frequent in asymptomatic (3/9) than in symptomatic (1/27) patients (P=0.016). Likewise, we found a highly significant association of TF expression with the occurrence of cerebral microembolism (P=0.008). CONCLUSIONS: Induction of TF at sites of plaque inflammation may play an important role in the destabilization of high-grade ICA stenosis.

Lymphocytic infiltration and expression of intercellular adhesion molecule-1 in photochemically induced ischemia of the rat cortex.

The contribution of the immune system to the pathogenesis of ischemic lesions is still uncertain. We have analyzed leukocyte infiltration in photochemically induced focal ischemia of the rat parietal cortex by immunocytochemistry. Between 1 and 2 days after photothrombosis, CD5+ T cells adhered to subpial and cortical vessels and infiltrated the ischemic lesion prior to macrophages. By day 3 numerous T cells and some macrophages, whose number increased further between day 3 and day 7, had infiltrated the border zone around the lesion sparing the center. In addition, CD5-/CD8+ lymphocytes that probably represent natural killer cells were found. Intercellular adhesion molecule-1 (ICAM-1) was expressed on endothelial cells on days 1 and 2 and in the border zone on infiltrating leukocytes from day 3 to day 7. Starting on day 7, macrophages infiltrated the core of the lesion to remove debris. When the entire lesion was covered by macrophages at day 14, the number of T cells had decreased and ICAM-1 immunoreactivity was no longer found in or around the infarct. In conclusion, our study shows that ischemic lesions can lead to a local immune reaction in the CNS. Thus, blocking of lymphocyte-derived cytokines or cell adhesion molecules may provide a new approach to confining the sequelae of stroke.

Cortical spreading depression induces proinflammatory cytokine gene expression in the rat brain.

Cortical spreading depression (CSD) is characterized by reversible neuronal dysfunction in the absence of cell death. Preconditioning by CSD induces tolerance against subsequent lethal ischemia. In this study, we used quantitative reverse transcriptase-polymerase chain reaction and immunocytochemistry to analyze proinflammatory cytokine expression after CSD induced by topical application of potassium chloride (KCl) to the cortical surface of rat brains. Relative to control cortex, we found an increase of tumor necrosis factor-alpha (mean 62-fold, P < 0.001) and interleukin (IL)-1beta (mean 24-fold, P < 0.001) mRNA levels within 4 hours ipsilateral to the site of KCl application. At 16 hours cytokine expression was decreasing toward baseline levels. Ipsilateral cytokine induction was abolished by pretreatment with the noncompetitive N-methyl-d-aspartate antagonist, MK-801. In contrast to focal cortical infarction, cytokine induction in CSD was not accompanied by the expression of inducible nitric oxide synthase mRNA. In immunocytochemical studies, expression of IL-1beta protein was localized to ramified microglia in cortical layers I to III of the ipsilateral hemisphere. Our finding that NMDA receptor signaling without subsequent neuronal cell death is sufficient to induce inflammatory cytokine expression in the brain has basic implications for central nervous system immunoregulation. We postulate that cytokine expression in CSD forms part of a physiologic stress response that contributes to the development of ischemic tolerance in this and other preconditioning paradigms.

Serum and CSF levels of soluble intercellular adhesion molecule-1 (ICAM-1) in inflammatory neurologic diseases.

Intercellular adhesion molecule-1 (ICAM-1), a cell surface receptor important for cellular interactions in immune responses, especially leukocyte trafficking into inflamed tissue, is released in a soluble form (sICAM-1) into the extracellular space. In this study, we measured sICAM-1 in paired serum and CSF samples from patients with inflammatory diseases of the nervous system (IND) and calculated a sICAM-1 index as a measure of the intrathecal release of ICAM-1. In comparison with noninflammatory neurologic disease (NIND) controls, we found increased sICAM-1 index levels in viral meningoencephalitis, bacterial meningitis and, to a lesser degree, multiple sclerosis but not in Guillain-Barré syndrome. Serial examination of viral meningoencephalitis patients in most cases showed a decrease of sICAM-1 index in parallel with falling cell counts and clinical improvement. Except for those in bacterial meningitis, sICAM-1 serum levels of IND patients were not significantly different from those of NIND controls. The increased intrathecal release of sICAM-1 in viral meningoencephalitis and bacterial meningitis most likely reflects activation of macrophages and lymphocytes and provides evidence for a strong local immune response that itself, in addition to the infectious agent, may damage nervous tissue.

Interleukin-18 is induced in acute inflammatory demyelinating polyneuropathy.

T lymphocytes of the Th1 subset producing the proinflammatory cytokine interferon-gamma (IFN-gamma) have been implicated in the pathogenesis of immune-mediated diseases of the peripheral nervous system (PNS) such as the acute Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN). Interleukin-18 (IL-18) is a potent IFN-gamma-inducing cytokine that is synthesized as an inactive precursor molecule and cleaved by caspase-1 into its mature active form. In our present study we analyzed the expression of IL-18 and caspase-1 in the nerve roots of EAN rats using reverse transcriptase-polymerase chain reaction and immunocytochemistry. Using an enzyme-linked immunosorbent assay, we furthermore determined IL-18 protein levels in paired serum and cerebrospinal fluid (CSF) samples from patients with GBS as well as from noninflammatory neurologic disease (NIND) controls. In EAN, IL-18 and caspase-1 mRNA levels in the nerve roots increased during the stage of active disease progression. Immunocytochemically, both perivascular and parenchymal IL-18 protein expression was increased in the roots of EAN rats and mainly associated with ED1+ macrophages stained on serial sections. IL-18 serum levels were significantly higher in GBS patients than in NIND controls (238+/-71 vs. 42+/-7 pg/ml, P<0.001). Our data implicate the Th1-inducing cytokine IL-18 in the pathogenesis of acute immune-mediated PNS demyelination.

Differential induction of interleukin-12, interleukin-18, and interleukin-1beta converting enzyme mRNA in experimental autoimmune encephalomyelitis of the Lewis rat.

Experimental autoimmune encephalomyelitis (EAE) is a model of autoimmune central nervous system (CNS) disease that is mediated by autoreactive Th1 cells secreting the proinflammatory cytokine interferon (IFN)-gamma. Interleukin (IL)-12 in its heterodimeric p35/p40 isoform and the recently described cytokine IL-18 potently induce T cell production of IFN-gamma. Interleukin-1beta converting enzyme (ICE) is required to convert IL-18 precursor protein into its biologically active mature form. In this study, we used semiquantitative reverse transciptase-polymerase chain reaction to determine steady state levels of IL-12, IL-18, and ICE mRNA in the spinal cord of Lewis rats at different stages of EAE. In control rats, we found significant IL-18, ICE, and IL-12p35, but not IL-12p40 mRNA expression. IL-18 mRNA increased during the acute stage of EAE together with a marked induction of ICE mRNA. IL-12p35 mRNA levels did not change significantly throughout the course of EAE. Surprisingly, the peak expression of IL-12p40 mRNA was delayed by several days relative to the peak of T cell infiltration and IFN-gamma mRNA synthesis. Our data implicate the IL-18/ICE pathway in the amplification of Th1-mediated immune responses in the CNS but suggest a different, so far undefined role of endogenous IL-12 in the late effector phase of EAE.

Role of NMDA receptor signaling in the regulation of inflammatory gene expression after focal brain ischemia.

Inflammatory mediators are involved in the pathogenesis of focal ischemic brain damage. In this study we used quantitative reverse transcriptase-polymerase chain reaction to analyze the spatiotemporal pattern of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and inducible nitric oxide synthase (iNOS) expression in focal ischemia of the rat brain. Focal ischemia of the rat parietal cortex was induced noninvasively by photothrombosis of cortical microvessels. In a proportion of the animals NMDA receptor signaling was blocked by the noncompetitive receptor antagonist MK-801. Within 4 h after ischemia we found induction of TNF-alpha and IL-1beta mRNA not only in the infarcts but also in all representative tissue samples removed from noninfarcted frontal, lateral, and occipital cortex of the ipsilateral, but not contralateral hemisphere. Contrastingly, the expression of iNOS mRNA remained restricted to the evolving infarcts. Pretreatment with MK-801 strongly inhibited remote cytokine expression (mean reduction by 80% relative to vehicle treated animals at 4 h; P<0.001) whereas in the lesions only partial reductions in the expression of IL-1beta and iNOS mRNA were found. Our data for the first time demonstrate remote cytokine induction following focal brain ischemia and suggest that NMDA receptor-mediated signaling can activate inflammatory gene expression independently from the occurrence of neuronal cell death.

Local immune responses in the rat cerebral cortex after middle cerebral artery occlusion.

This study describes local immune responses in cerebral ischemia induced by permanent occlusion of the middle cerebral artery (MCAO) in the rat. The temporal and spatial pattern of leukocyte infiltration was characterized immunocytochemically using monoclonal antibodies against CD5, a pan T cell marker, against CD4 and CD8 for subtyping of T lymphocytes, and ED1, a marker for macrophages. CD5+ T cells were present in some animals on the pial surface at day 1 and with increasing numbers mainly at the edges of the infarcts at days 3 and 7. By day 14 their number had significantly decreased. Subtyping of T lymphocytes revealed that CD4+ helper/inducer T cells were rare, while CD8+ lymphocytes were abundant. Moreover, CD8+ lymphocytes outnumbered CD5+ T cells indicating the presence of CD5-/CD8+ natural killer (NK) cells. ED1+ macrophages primarily infiltrated the core of the infarct starting on day 1. Infiltrating leukocytes expressed leukocyte function associated antigen-1 and MHC class I and II antigens. Early after infarction, increased expression of the intercellular adhesion molecule-1 was found on vessels and leukocytes. In conclusion, this study shows that lymphocytes enter the nervous system not only in autoimmune diseases, but also in response to primarily 'non-immune' neuronal damage such as stroke.

Serum and cerebrospinal fluid levels of soluble intercellular adhesion molecule 1 (sICAM-1) in patients with HIV-1 associated neurological diseases.

We measured levels of soluble intercellular adhesion molecule 1 (sICAM-1) in paired serum and CSF samples of 110 HIV-1-positive patients with and without neurological symptoms and 40 HIV-negative non-immune neurological controls, and in sera of 26 asymptomatic HIV-1-positive patients. Serum sICAM-1 levels in asymptomatic HIV-1-positive patients were significantly increased in comparison to HIV-negative controls. Moreover, they were significantly higher in HIV-1-positive patients with AIDS-defining diseases than in the asymptomatic HIV-1-positive group. In subgroups of patients with neurological disease, the highest serum values were found in HIV encephalopathy. CSF levels of sICAM-1 were elevated only in HIV-1-positive patients with neurological disease mainly due to passive diffusion through a defective blood-brain barrier. An sICAM-1 index was calculated as a measure for intrathecal production of sICAM-1 but showed no significant differences between patients with and without neurological involvement. However, increased levels of the sICAM-1 index were found in some patients with opportunistic CNS infection of bacterial or fungal origin. Serum and CSF levels of sICAM-1 correlated with neopterin levels, a marker of interferon-gamma-mediated macrophage activation and CSF sICAM-1 levels were inversely correlated to numbers of CD4+ T cells. Elevated serum sICAM-1 levels already in asymptomatic HIV-1-positive individuals add to the evidence for an early immune activation in HIV infection. With the further increase of serum and CSF s-ICAM-1 in patients with AIDS-defining diseases sICAM-1 could serve as a new surrogate marker similar to neopterin.

Vascular cell adhesion molecule-1 mRNA is expressed in immune-mediated and ischemic injury of the rat nervous system.

In this study we used nonradioactive in situ hybridization for the cellular localization of vascular cell adhesion molecule-1 (VCAM-1) mRNA in immune-mediated, ischemic and degenerative diseases of the rat nervous system. In the acute phase of experimental autoimmune encephalomyelitis and neuritis VCAM-1 mRNA was expressed not only on the luminal surface of inflamed vessels but also in perivascular cells suggesting a functional role of VCAM-1 in both endothelial adhesion and local restimulation of autoantigen-specific T cells. Accordingly, perivascular T cell accumulation was most pronounced at sites of local VCAM-1 mRNA expression. In addition, VCAM-1 mRNA was detected in the border zone around photochemically induced cerebral infarcts which is the predeliction site of T cell infiltration and expression of immune activation markers during the first week after ischemia. VCAM-1 mRNA was absent from the center of the infarcts as well as axotomized central and peripheral nerves undergoing Wallerian degeneration. These data indicate that VCAM-1-mediated adhesion processes are involved in immune-mediated and ischemic diseases of the nervous system but not in T cell-independent macrophage recruitment during Wallerian degeneration.

Tumor necrosis factor-alpha in immune-mediated demyelination and Wallerian degeneration of the rat peripheral nervous system.

This study reports on the immunocytochemical localization of tumor necrosis factor-alpha (TNF alpha) in immune-mediated demyelination and Wallerian degeneration of the rat peripheral nervous system (PNS) using teased nerve fiber preparations. In experimental autoimmune neuritis induced by active immunization (EAN) or by adoptive transfer of autoreactive T cells (AT-EAN), macrophages passing blood vessels as well as macrophages adherent to nerve fibers were TNF alpha-positive. Large post-phagocytic macrophages at later stages of demyelination were TNF alpha-negative. Intraperitoneal application of an anti-TNF alpha antibody to EAN rats significantly reduced the degree of inflammatory demyelination, suggesting a pathogenic role for TNF alpha. After nerve transection only macrophages located within degenerating nerve fibers were TNF alpha-positive, while those entering and leaving nerves were negative. TNF alpha produced by macrophages seems to be involved in immune-mediated demyelination and non-immune myelin degradation after axotomy. While interferon-gamma (IFN gamma) is present in EAN nerves and may act as a local stimulus for TNF expression, the nature of this signal in Wallerian degeneration in the absence of IFN gamma is unknown.

Heterogeneity of the microglial response in photochemically induced focal ischemia of the rat cerebral cortex.

This study examined microglial responses after photochemically induced focal ischemia of the rat cortex. Microglial activation exceeded by far the area of the ischemic lesion. Based on morphological criteria and expression of immunomolecules three distinct patterns could be distinguished. (1) In the infarct core and the border zone microglia transformed into phagocytes and removed debris with the aid of hematogeneous macrophages. Exclusively in this area a subpopulation of CD8+ microglia/mnacrophages was present. (2) In secondarily degenerating fibre tracts and nuclei with retrograde neuronal loss, microglia were activated with a delay of days and showed increased expression of complement receptor 3, major histocompatibility complex class II and CD4 molecules, but only low phagocytic activity. (3) In remote ipsilateral cortex devoid of neuronal damage, microglia transiently responded by increased complement receptor 3, but not by major histocompatibility complex class II and CD4 expression. Furthermore, the total number of microglia had increased. This remote response could partly be blocked by dizocilpine maleate, a non-competitive N-methyl-D-aspartate receptor antagonist, implicating a functional role of spreading depression. Taken together, our findings point to a tight and differential regulation of microglial responses in the infarct core, degenerating fibre tracts and remote brain regions without neuronal loss.

Time course of inwardly rectifying K(+) current reduction in glial cells surrounding ischemic brain lesions.

K(+) currents of activated glial cells surrounding ischemic infarcts are investigated using acutely dissociated cells from the periinfarct area after permanent middle cerebral artery occlusion in rats. Inwardly rectifying K(+) currents (K(IR)) were markedly reduced in cells neighboring infarcts with maximal alteration at day 3 after infarct followed by a partial recovery. This reduction of glial K(IR) currents may contribute to the functional disturbances in the periinfarct area.

Cytokines in CNS disorders: neurotoxicity versus neuroprotection.

Cytokines orchestrate T cell-mediated immune responses. In experimental autoimmune encephalomyelitis (EAE) the proinflammatory cytokines interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, IL-12 and IL-18 are critically involved in the initiation and amplification of the local immune response in the CNS which is counter-balanced by upregulation of antiinflammatory cytokines such as IL-10. The predicted function of individual cytokines during EAE has recently been challenged by transgenic animal studies and neutralization experiments. Cytokine induction is not restricted to autoimmunity in the nervous system. Cytokines are involved in nerve regeneration and induced in focal cerebral ischemia both at the site of infarction and in remote nonischemic brain regions. In cerebral ischemia TNF-alpha and IL-1beta probably have dual functions: In concert with upregulation of inducible NO synthase (iNOS) they exert neurotoxicity while in the absence of iNOS, TNF-alpha and IL-1beta may contribute to neuroprotection and plasticity. The interplay between glial cells, infiltrating leukocytes and induced cytokines leading to CNS pathology is complex and incompletely understood. Further assessment of the functional contribution of cytokines critically depends on the elucidation of downstream secondary signaling mechanisms.