Fcgamma receptor I- and III-mediated macrophage inflammatory protein 1alpha induction in primary human and murine microglia

How brain 'cleaners' fail: Mechanisms and therapeutic value of microglial phagocytosis in Alzheimer's disease

Microglia are the resident phagocytes of the brain, where they primarily function in the clearance of dead cells and the removal of un- or misfolded proteins. The impaired activity of receptors or proteins involved in phagocytosis can result in enhanced inflammation and neurodegeneration. RNA-seq and genome-wide association studies have linked multiple phagocytosis-related genes to neurodegenerative diseases, while the knockout of such genes has been demonstrated to exert protective effects against neurodegeneration in animal models. The failure of microglial phagocytosis influences AD-linked pathologies, including amyloid β accumulation, tau propagation, neuroinflammation, and infection. However, a precise understanding of microglia-mediated phagocytosis in Alzheimer's disease (AD) is still lacking. In this review, we summarize current knowledge of the molecular mechanisms involved in microglial phagocytosis in AD across a wide range of pre-clinical, post-mortem, ex vivo, and clinical studies and review the current limitations regarding the detection of microglia phagocytosis in AD. Finally, we discuss the rationale of targeting microglial phagocytosis as a therapeutic strategy for preventing AD or slowing its progression.

Increased levels of a pro-inflammatory IgG receptor in the midbrain of people with schizophrenia

BACKGROUND

There is growing evidence that neuroinflammation may contribute to schizophrenia neuropathology. Elevated pro-inflammatory cytokines are evident in the midbrain from schizophrenia subjects, findings that are driven by a subgroup of patients, characterised as a "high inflammation" biotype. Cytokines trigger the release of antibodies, of which immunoglobulin G (IgG) is the most common. The level and function of IgG is regulated by its transporter (FcGRT) and by pro-inflammatory IgG receptors (including FcGR3A) in balance with the anti-inflammatory IgG receptor FcGR2B. Testing whether abnormalities in IgG activity contribute to the neuroinflammatory abnormalities schizophrenia patients, particularly those with elevated cytokines, may help identify novel treatment targets.

METHODS

Post-mortem midbrain tissue from healthy controls and schizophrenia cases (n = 58 total) was used to determine the localisation and abundance of IgG and IgG transporters and receptors in the midbrain of healthy controls and schizophrenia patients. Protein levels of IgG and FcGRT were quantified using western blot, and gene transcript levels of FcGRT, FcGR3A and FcGR2B were assessed using qPCR. The distribution of IgG in the midbrain was assessed using immunohistochemistry and immunofluorescence. Results were compared between diagnostic (schizophrenia vs control) and inflammatory (high vs low inflammation) groups.

RESULTS

We found that IgG and FcGRT protein abundance (relative to β-actin) was unchanged in people with schizophrenia compared with controls irrespective of inflammatory subtype. In contrast, FcGRT and FcGR3A mRNA levels were elevated in the midbrain from "high inflammation" schizophrenia cases (FcGRT; p = 0.02, FcGR3A; p < 0.0001) in comparison to low-inflammation patients and healthy controls, while FcGR2B mRNA levels were unchanged. IgG immunoreactivity was evident in the midbrain, and approximately 24% of all individuals (control subjects and schizophrenia cases) showed diffusion of IgG from blood vessels into the brain. However, the intensity and distribution of IgG was comparable across schizophrenia cases and control subjects.

CONCLUSION

These findings suggest that an increase in the pro-inflammatory Fcγ receptor FcGR3A, rather than an overall increase in IgG levels, contribute to midbrain neuroinflammation in schizophrenia patients. However, more precise information about IgG-Fcγ receptor interactions is needed to determine their potential role in schizophrenia neuropathology.

Insights into the Pathogenesis of Neurodegenerative Diseases: Focus on Mitochondrial Dysfunction and Oxidative Stress

As the population ages, the incidence of neurodegenerative diseases is increasing. Due to intensive research, important steps in the elucidation of pathogenetic cascades have been made and significantly implicated mitochondrial dysfunction and oxidative stress. However, the available treatment in Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis is mainly symptomatic, providing minor benefits and, at most, slowing down the progression of the disease. Although in preclinical setting, drugs targeting mitochondrial dysfunction and oxidative stress yielded encouraging results, clinical trials failed or had inconclusive results. It is likely that by the time of clinical diagnosis, the pathogenetic cascades are full-blown and significant numbers of neurons have already degenerated, making it impossible for mitochondria-targeted or antioxidant molecules to stop or reverse the process. Until further research will provide more efficient molecules, a healthy lifestyle, with plenty of dietary antioxidants and avoidance of exogenous oxidants may postpone the onset of neurodegeneration, while familial cases may benefit from genetic testing and aggressive therapy started in the preclinical stage.

Alzheimer's Disease Pathogenesis: Role of Autophagy and Mitophagy Focusing in Microglia

Alzheimer's disease (AD) is a debilitating neurological disorder, and currently, there is no cure for it. Several pathologic alterations have been described in the brain of AD patients, but the ultimate causative mechanisms of AD are still elusive. The classic hallmarks of AD, including amyloid plaques (Aβ) and tau tangles (tau), are the most studied features of AD. Unfortunately, all the efforts targeting these pathologies have failed to show the desired efficacy in AD patients so far. Neuroinflammation and impaired autophagy are two other main known pathologies in AD. It has been reported that these pathologies exist in AD brain long before the emergence of any clinical manifestation of AD. Microglia are the main inflammatory cells in the brain and are considered by many researchers as the next hope for finding a viable therapeutic target in AD. Interestingly, it appears that the autophagy and mitophagy are also changed in these cells in AD. Inside the cells, autophagy and inflammation interact in a bidirectional manner. In the current review, we briefly discussed an overview on autophagy and mitophagy in AD and then provided a comprehensive discussion on the role of these pathways in microglia and their involvement in AD pathogenesis.

Therapeutic Potential of Neu1 in Alzheimer's Disease Via the Immune System

Alzheimer's Disease (AD) is pathologically characterized by the accumulation of soluble oligomers causing extracellular beta-amyloid deposits in form of neuritic plaques and tau-containing intraneuronal neurofibrillary tangles in brain. One proposed mechanism explaining the formation of these proteins is impaired phagocytosis by microglia/macrophages resulting in defective clearance of soluble oligomers of beta-amyloid stimulating aggregation of amyloid plaques subsequently causing AD. However, research indicates that activating macrophages in M2 state may reduce toxic oligomers. NEU1 mutation is associated with a rare disease, sialidosis. NEU1 deficiency may also cause AD-like amyloidogenic process. Amyloid plaques have successfully been reduced using NEU1.Thus, NEU1 is suggested to have therapeutic potential for AD, with lysosomal exocytosis being suggested as underlying mechanism. Studies however demonstrate that NEU1 may activate macrophages in M2 state, which as noted earlier, is crucial to reducing toxic oligomers. In this review, authors discuss the potential therapeutic role of NEU1 in AD via immune system.

The Role of Macrophages in Neuroinflammatory and Neurodegenerative Pathways of Alzheimer's Disease, Amyotrophic Lateral Sclerosis, and Multiple Sclerosis: Pathogenetic Cellular Effectors and Potential Therapeutic Targets

In physiological conditions, different types of macrophages can be found within the central nervous system (CNS), i.e., microglia, meningeal macrophages, and perivascular (blood-brain barrier) and choroid plexus (blood-cerebrospinal fluid barrier) macrophages. Microglia and tissue-resident macrophages, as well as blood-borne monocytes, have different origins, as the former derive from yolk sac erythromyeloid precursors and the latter from the fetal liver or bone marrow. Accordingly, specific phenotypic patterns characterize each population. These cells function to maintain homeostasis and are directly involved in the development and resolution of neuroinflammatory processes. Also, following inflammation, circulating monocytes can be recruited and enter the CNS, therefore contributing to brain pathology. These cell populations have now been identified as key players in CNS pathology, including autoimmune diseases, such as multiple sclerosis, and degenerative diseases, such as Amyotrophic Lateral Sclerosis and Alzheimer’s disease. Here, we review the evidence on the involvement of CNS macrophages in neuroinflammation and the advantages, pitfalls, and translational opportunities of pharmacological interventions targeting these heterogeneous cellular populations for the treatment of brain diseases.

Therapeutic Potential of Intravenous Immunoglobulin in Acute Brain Injury

Acute ischemic and traumatic injury of the central nervous system (CNS) is known to induce a cascade of inflammatory events that lead to secondary tissue damage. In particular, the sterile inflammatory response in stroke has been intensively investigated in the last decade, and numerous experimental studies demonstrated the neuroprotective potential of a targeted modulation of the immune system. Among the investigated immunomodulatory agents, intravenous immunoglobulin (IVIg) stand out due to their beneficial therapeutic potential in experimental stroke as well as several other experimental models of acute brain injuries, which are characterized by a rapidly evolving sterile inflammatory response, e.g., trauma, subarachnoid hemorrhage. IVIg are therapeutic preparations of polyclonal immunoglobulin G, extracted from the plasma of thousands of donors. In clinical practice, IVIg are the treatment of choice for diverse autoimmune diseases and various mechanisms of action have been proposed. Only recently, several experimental studies implicated a therapeutic potential of IVIg even in models of acute CNS injury, and suggested that the immune system as well as neuronal cells can directly be targeted by IVIg. This review gives further insight into the role of secondary inflammation in acute brain injury with an emphasis on stroke and investigates the therapeutic potential of IVIg.

Immune suppression of IgG response against dairy proteins in major depression

BACKGROUND

Interactions between the digestive system, brain functions and immunoglobulin G (IgG) mediated immunity against food antigens became recently a topic of growing interest in psychiatry research. Psychological stress can activate hypothalamic-pituitary-adrenal axis (HPA) with subsequent hypercortisolemia. It can also influence intestinal permeability and dynamics of IgG response. Major depression can by accompanied either by activation of inflammatory response or by immune suppression (e.g. decreased antibody production) where hypercortisolemia is a significant immune modulator. The aim of our study was to assess IgG immune response against 44 food products in depressed patients and controls along with markers of psychological stress, inflammation, psychometric and dietary parameters.

METHODS

Serum IgG concentrations against 44 food antigens, plasma cortisol, TNF-α, IL-6, IL-1b concentrations were measured and psychometric parameters were evaluated using Hamilton Depression Rating (HAM-D 17), Perceived Stress (PSS-10), and Symptom Checklist (SCL-90) scales in 34 depressed patients and 29 controls. Dietary parameters such as frequency of exposure to food antigens, appetite and weight change were assessed.

RESULTS

There was a significantly lower IgG concentration against dairy in depressed patients compared to controls (post hoc p < 0.05) when there was a high exposure (consumption) to dairy. Our research revealed a significant interaction of IgG concentration against dairy proteins and exposure to dairy between groups (F (2.63) = 3.92, p = 0.025, η² = 0.12). There was no significant difference in mean IgG concentration against food antigens between patients and controls. We found increased concentration of cortisol in depressed patients (t (1.61) = 2.37, p = 0.02) compared to controls. Patients with melancholic depression had significantly higher (M _rank  = 21.27) concentration of cortisol (U = 41, p = 0.006), when compared with the non-melancholic group of patients (M _rank  = 12.16). Cortisol concentration significantly positively correlated with HAM-D 17 (r = 0.442, p = 0.009) and with phobias in SCL-90 scale in patients' group (r = 0.531, p = 0.001). There was decreased concentration of TNF-α (t = 4.256, p < 0.001) in depressed patients compared to controls. IgG concentration of 38.63% food products positively correlated with TNF-α concentration in depressed patients compared to 9.09% of those in healthy controls.

CONCLUSIONS

We observed an immune suppression of IgG response to dairy proteins in depressed patients. Hypercortisolemia with involvement of decreased concentration of TNF-α might play a significant role in suppression of IgG response in depressed patients.

Blood-brain barrier disruption during spontaneous canine visceral leishmaniasis

Visceral leishmaniasis is a complex disease caused by Leishmania infantum, and in dogs, besides the classical symptoms, there are descriptions of inflammatory alterations in the brain. Brain inflammation is a strictly controlled process, and as the brain counts on the efficiency of the blood-brain barrier (BBB), we aimed to assess BBB integrity in dogs with spontaneous visceral leishmaniasis. Therefore, we evaluated markers in the cerebrospinal fluid (CSF) and in brain tissue related to BBB disruption and brain inflammation. Elevated albumin quota revealed BBB breakdown, corroborated by increased concentrations of anti-Leishmania antibodies in the CSF. In the brain, albumin and IgG staining formed halos around blood vessels, a classical indicator of BBB leakage. Soluble IgG was also detected in the choroid plexus and ependyma, and in these structures, IgG stained random resident cells. IgG(+) cells and Fcγ-RI(+) cells were identified in the choroid plexus, ependyma and perivascular in the brain parenchyma. The data support the occurrence of BBB disruption in dogs with spontaneous visceral leishmaniasis, and IgG as a key molecule that is capable of initiating and/or maintaining the inflammatory stimuli in the nervous milieu and the CSF as an important disseminator of inflammatory stimuli within the CNS.

Flow cytometric characterization of microglia in the offspring of PolyI:C treated mice

The neuropathology of schizophrenia has been reported to be closely associated with microglial activation. In a previous study, using the prenatal PolyI:C schizophrenia animal model, we showed an increase in cell numbers and a reduction in microglial branching in 30-day-old PolyI:C descendants, which suggests that there is microglial activation during adolescence. To provide more information about the activation state, we aimed to examine the expression levels of Iba1, which was reported to be up-regulated in activated microglia. We used a flow cytometric approach and investigated CD11b and CD45, two additional markers for the identification of microglial cells. We demonstrated that intracellular staining against Iba1 can be used as a reliable flow cytometric method for identification of microglial cells. Prenatal PolyI:C treatment had long-term effects on CD11b and CD45 expression. It also resulted in a trend towards increased Iba1 expression. Imbalance in CD11b, CD45, and Iba1 expression might contribute to impaired synaptic surveillance and enhanced activation/inflammatory activity of microglia in adult offspring.

A chimeric Cfh transgene leads to increased retinal oxidative stress, inflammation, and accumulation of activated subretinal microglia in mice

PURPOSE

Variants of complement factor H (Cfh) affecting short consensus repeats (SCRs) 6 to 8 increase the risk of age-related macular degeneration. Our aim was to explore the effect of expressing a Cfh variant on the in vivo susceptibility of the retina and RPE to oxidative stress and inflammation, using chimeric Cfh transgenic mice (chCfhTg).

METHODS

The chCfhTg and age-matched C57BL/6J (B6) mice were subjected to oxidative stress by either normal aging, or by exposure to a combination of oral hydroquinone (0.8% HQ) and increased light. Eyes were collected for immunohistochemistry of RPE-choroid flat mounts and of retinal sections, ELISA, electron microscopy, and RPE/microglia gene expression analysis.

RESULTS

Aging mice to 2 years led to an increased accumulation of basal laminar deposits, subretinal microglia/macrophages (MG/MΦ) staining for CD16 and for malondialdehyde (MDA), and MDA-modified proteins in the retina in chCfhTg compared to B6 mice. The chCfhTg mice maintained on HQ diet and increased light showed greater deposition of basal laminar deposits, more accumulation of fundus spots suggestive of MG/MΦ, and increased deposition of C3d in the sub-RPE space, compared to controls. In addition, chCfhTg mice demonstrated upregulation of NLRP3, IP-10, CD68, and TREM-2 in the RNA isolates from RPE/MG/MΦ.

CONCLUSIONS

Expression of a Cfh transgene introducing a variant in SCRs 6 to 8 was sufficient to lead to increased retinal/RPE susceptibility to oxidative stress, a proinflammatory MG/MΦ phenotype, and a proinflammatory RPE/MG/MΦ gene expression profile in a transgenic mouse model. Our data suggest that altered interactions of Cfh with MDA-modified proteins may be relevant in explaining the effects of the Cfh variant.

Fungal colonization of the brain: anatomopathological aspects of neurological cryptococcosis

Brain infection by the fungus Cryptococcus neoformans results in an estimated 500,000 human deaths per annum. Colonization of the central nervous system (CNS) by C. neoformans causes different clinical syndromes that involve interaction of a number of fungal components with distinct brain cells. In this manuscript, our literature review confirmed the notion that the Cryptococcus field is expanding rapidly, but also suggested that studies on neuropathogenesis still represent a small fraction of basic research activity in the field. We therefore discussed anatomical and physiological aspects of the brain during infection by C. neoformans, in addition to mechanisms by which brain resident cells interact with the fungus. This review suggests that multiple efforts are necessary to improve the knowledge on how C. neoformans affects brain cells, in order to enable the generation of new therapeutic tools in a near future.

Isolation of vascular endothelial cells from intact and injured murine brain cortex-technical issues and pitfalls in FACS analysis of the nervous tissue

CNS endothelial cells (CNS-ECs), one of the main non-neural CNS cell populations, play a vital role in physiology, pathology, and regeneration of the nervous system. Therefore, there is an urgent need to enhance our knowledge on their biology to elucidate mechanisms responsible for the blood brain barrier function in normal and pathological conditions, interaction between brain endothelium and neural stem cells in the neurogenic niche, the paracrine processes in the brain and spinal cord, etc. Here, we described a novel, simple, and efficient protocol for isolation of endothelial, vessel-forming cells from the murine CNS, which is based on Sca-1 expression. Using this newly described protocol we were able to detect and sort viable, highly pure CNS-ECs with minimal contamination by cells of non-endothelial origin. This method will increase the availability of CNS-ECs for in vitro research. Moreover, we compared phenotype of CNS-ECs isolated from neonatal mice and adult intact and injured brain looking for the cells of endothelial precursor characteristic, such as those found in the bone marrow and circulating in the bloodstream after organ injuries. We have found that neonatal brain capillaries contain proportion of endothelial precursor cells (Sca-1(+) , CD45(-) , c-Kit(+) ). Such precursors were also found in adult brain cortex, both in intact and injured brain. Finally, we discuss several crucial technical issues concerning CNS tissue preparation for flow cytometry analysis and cell sorting as well as nonspecific antibody binding caused by inflammatory microglia/macrophages which should be avoided in order to reliable isolation of pure CNS cells for downstream procedures including cell transplantation-based translational studies.

Neurobiology of microglial action in CNS injuries: receptor-mediated signaling mechanisms and functional roles

Microglia are the first line of immune defense against central nervous system (CNS) injuries and disorders. These highly plastic cells play dualistic roles in neuronal injury and recovery and are known for their ability to assume diverse phenotypes. A broad range of surface receptors are expressed on microglia and mediate microglial 'On' or 'Off' responses to signals from other host cells as well as invading microorganisms. The integrated actions of these receptors result in tightly regulated biological functions, including cell mobility, phagocytosis, the induction of acquired immunity, and trophic factor/inflammatory mediator release. Over the last few years, significant advances have been made toward deciphering the signaling mechanisms related to these receptors and their specific cellular functions. In this review, we describe the current state of knowledge of the surface receptors involved in microglial activation, with an emphasis on their engagement of distinct functional programs and their roles in CNS injuries. It will become evident from this review that microglial homeostasis is carefully maintained by multiple counterbalanced strategies, including, but not limited to, 'On' and 'Off' receptor signaling. Specific regulation of theses microglial receptors may be a promising therapeutic strategy against CNS injuries.

IgG response to intracerebral xenotransplantation: specificity and role in the rejection of porcine neurons

Xenogenic fetal neuroblasts are considered as a potential source of transplantable cells for the treatment of neurodegenerative diseases, but immunological barriers limit their use in the clinic. While considerable work has been performed to decipher the role of the cellular immune response in the rejection of intracerebral xenotransplants, there is much still to learn about the humoral reaction. To this end, the IgG response to the transplantation of fetal porcine neural cells (PNC) into the rat brain was analyzed. Rat sera did not contain preformed antibodies against PNC, but elicited anti-porcine IgG was clearly detected in the host blood once the graft was rejected. Only the IgG1 and IgG2a subclasses were up-regulated, suggesting a T-helper 2 immune response. The main target of these elicited IgG antibodies was porcine neurons, as determined by double labeling in vitro and in vivo. Complement and anti-porcine IgG were present in the rejecting grafts, suggesting an active role of the host humoral response in graft rejection. This hypothesis was confirmed by the prolonged survival of fetal porcine neurons in the striatum of immunoglobulin-deficient rats. These data suggest that the prolonged survival of intracerebral xenotransplants relies on the control of both cell-mediated and humoral immune responses.

Microglia receptors and their implications in the response to amyloid β for Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a major public health problem with substantial economic and social impacts around the world. The hallmarks of AD pathogenesis include deposition of amyloid β (Aβ), neurofibrillary tangles, and neuroinflammation. For many years, research has been focused on Aβ accumulation in senile plaques, as these aggregations were perceived as the main cause of the neurodegeneration found in AD. However, increasing evidence suggests that inflammation also plays a critical role in the pathogenesis of AD. Microglia cells are the resident macrophages of the brain and act as the first line of defense in the central nervous system. In AD, microglia play a dual role in disease progression, being essential for clearing Aβ deposits and releasing cytotoxic mediators. Aβ activates microglia through a variety of innate immune receptors expressed on these cells. The mechanisms through which amyloid deposits provoke an inflammatory response are not fully understood, but it is believed that these receptors cooperate in the recognition, internalization, and clearance of Aβ and in cell activation. In this review, we discuss the role of several receptors expressed on microglia in Aβ recognition, uptake, and signaling, and their implications for AD pathogenesis.

Paroxetine ameliorates lipopolysaccharide-induced microglia activation via differential regulation of MAPK signaling

BACKGROUND

Paroxetine, a selective serotonin reuptake inhibitor for counteracting depression, has been recently suggested as having a role in prevention of dopaminergic neuronal degeneration in substantia nigra, a hallmark of Parkinson's disease (PD). The pathogenesis of this type of neurological disorders often involves the activation of microglia and associated inflammatory processes. Thus in this study we aimed to understand the role of paroxetine in microglia activation and to elucidate the underlying mechanism(s).

METHODS

BV2 and primary microglial cells were pretreated with paroxetine and stimulated with lipopolysaccharide (LPS). Cells were assessed for the responses of pro-inflammatory mediator and cytokines, and the related signaling pathways were evaluated and analyzed in BV2 cells.

RESULTS

Paroxetine significantly inhibited LPS-induced production of nitric oxide (NO) and pro-inflammatory cytokines such as TNF-α and IL-1β. Further analysis showed inducible nitric oxide synthase (iNOS) and mRNA expression of TNF-α and IL-1β were attenuated by paroxetine pretreatment. Analyses in signaling pathways demonstrated that paroxetine led to suppression of LPS-induced JNK1/2 activation and baseline ERK1/2 activity, but had little effect on the activation of p38 and p65/NF-κB. Interference with specific inhibitors revealed that paroxetine-mediated suppression of NO production was via JNK1/2 pathway while the cytokine suppression was via both JNK1/2 and ERK1/2 pathways. Furthermore, conditioned media culture showed that paroxetine suppressed the microglia-mediated neurotoxicity.

CONCLUSIONS

Paroxetine inhibits LPS-stimulated microglia activation through collective regulation of JNK1/2 and ERK1/2 signaling. Our results indicate a potential role of paroxetine in neuroprotection via its anti-neuroinflammatory effect besides targeting for depression.

Neuron-derived IgG protects dopaminergic neurons from insult by 6-OHDA and activates microglia through the FcγR I and TLR4 pathways

Oxidative and immune attacks from the environment or microglia have been implicated in the loss of dopaminergic neurons of Parkinson's disease. The role of IgG which is an important immunologic molecule in the process of Parkinson's disease has been unclear. Evidence suggests that IgG can be produced by neurons in addition to its traditionally recognized source B lymphocytes, but its function in neurons is poorly understood. In this study, extensive expression of neuron-derived IgG was demonstrated in dopaminergic neurons of human and rat mesencephalon. With an in vitro Parkinson's disease model, we found that neuron-derived IgG can improve the survival and reduce apoptosis of dopaminergic neurons induced by 6-hydroxydopamine toxicity, and also depress the release of NO from microglia triggered by 6-hydroxydopamine. Expression of TNF-α and IL-10 in microglia was elevated to protective levels by neuron-derived IgG at a physiologic level via the FcγR I and TLR4 pathways and microglial activation could be attenuated by IgG blocking. All these data suggested that neuron-derived IgG may exert a self-protective function by activating microglia properly, and IgG may be involved in maintaining immunity homeostasis in the central nervous system and serve as an active factor under pathological conditions such as Parkinson's disease.

HLA class I antibodies trigger increased adherence of monocytes to endothelial cells by eliciting an increase in endothelial P-selectin and, depending on subclass, by engaging FcγRs

Ab-mediated rejection (AMR) of solid organ transplants is characterized by intragraft macrophages. It is incompletely understood how donor-specific Ab binding to graft endothelium promotes monocyte adhesion, and what, if any, contribution is made by the Fc region of the Ab. We investigated the mechanisms underlying monocyte recruitment by HLA class I (HLA I) Ab-activated endothelium. We used a panel of murine mAbs of different subclasses to crosslink HLA I on human aortic, venous, and microvascular endothelial cells and measured the binding of human monocytic cell lines and peripheral blood monocytes. Both anti-HLA I murine (m)IgG1 and mIgG2a induced endothelial P-selectin, which was required for monocyte adhesion to endothelium irrespective of subclass. mIgG2a but not mIgG1 could bind human FcγRs. Accordingly, HLA I mIgG2a but not mIgG1 treatment of endothelial cells significantly augmented recruitment, predominantly through FcγRI, and, to a lesser extent, FcγRIIa. Moreover, HLA I mIgG2a promoted firm adhesion of monocytes to ICAM-1 through Mac-1, which may explain the prominence of monocytes during AMR. We confirmed these observations using human HLA allele-specific mAbs and IgG purified from transplant patient sera. HLA I Abs universally elicit endothelial exocytosis leading to monocyte adherence, implying that P-selectin is a putative therapeutic target to prevent macrophage infiltration during AMR. Importantly, the subclass of donor-specific Ab may influence its pathogenesis. These results imply that human IgG1 and human IgG3 should have a greater capacity to trigger monocyte infiltration into the graft than IgG2 or IgG4 due to enhancement by FcγR interactions.

Immunoglobulin G Fc receptor deficiency prevents Alzheimer-like pathology and cognitive impairment in mice

Alzheimer's disease is a severely debilitating disease of high and growing proportions. Hypercholesterolaemia is a key risk factor in sporadic Alzheimer's disease that links metabolic disorders (diabetes, obesity and atherosclerosis) with this pathology. Hypercholesterolaemia is associated with increased levels of immunoglobulin G against oxidized lipoproteins. Patients with Alzheimer's disease produce autoantibodies against non-brain antigens and specific receptors for the constant Fc region of immunoglobulin G have been found in vulnerable neuronal subpopulations. Here, we focused on the potential role of Fc receptors as pathological players driving hypercholesterolaemia to Alzheimer's disease. In a well-established model of hypercholesterolaemia, the apolipoprotein E knockout mouse, we report increased brain levels of immunoglobulin G and upregulation of activating Fc receptors, predominantly of type IV, in neurons susceptible to amyloid β accumulation. In these mice, gene deletion of γ-chain, the common subunit of activating Fc receptors, prevents learning and memory impairments without influencing cholesterolaemia and brain and serum immunoglobulin G levels. These cognition-protective effects were associated with a reduction in synapse loss, tau hyperphosphorylation and intracellular amyloid β accumulation both in cortical and hippocampal pyramidal neurons. In vitro, activating Fc receptor engagement caused synapse loss, tau hyperphosphorylation and amyloid β deposition in primary neurons by a mechanism involving mitogen-activated protein kinases and β-site amyloid precursor protein cleaving enzyme 1. Our results represent the first demonstration that immunoglobulin G Fc receptors contribute to the development of hypercholesterolaemia-associated features of Alzheimer's disease and suggest a new potential target for slowing or preventing Alzheimer's disease in hypercholesterolaemic patients.

The NS1 glycoprotein can generate dramatic antibody-enhanced dengue viral replication in normal out-bred mice resulting in lethal multi-organ disease

Antibody-enhanced replication (AER) of dengue type-2 virus (DENV-2) strains and production of antibody-enhanced disease (AED) was tested in out-bred mice. Polyclonal antibodies (PAbs) generated against the nonstructural-1 (NS1) glycoprotein candidate vaccine of the New Guinea-C (NG-C) or NSx strains reacted strongly and weakly with these antigens, respectively. These PAbs contained the IgG2a subclass, which cross-reacted with the virion-associated envelope (E) glycoprotein of the DENV-2 NSx strain, suggesting that they could generate its AER via all mouse Fcγ-receptor classes. Indeed, when these mice were challenged with a low dose (<0.5 LD₅₀) of the DENV-2 NSx strain, but not the NG-C strain, they all generated dramatic and lethal DENV-2 AER/AED. These AER/AED mice developed life-threatening acute respiratory distress syndrome (ARDS), displayed by diffuse alveolar damage (DAD) resulting from i) dramatic interstitial alveolar septa-thickening with mononuclear cells, ii) some hyperplasia of alveolar type-II pneumocytes, iii) copious intra-alveolar protein secretion, iv) some hyaline membrane-covered alveolar walls, and v) DENV-2 antigen-positive alveolar macrophages. These mice also developed meningo-encephalitis, with greater than 90,000-fold DENV-2 AER titers in microglial cells located throughout their brain parenchyma, some of which formed nodules around dead neurons. Their spleens contained infiltrated megakaryocytes with DENV-2 antigen-positive red-pulp macrophages, while their livers displayed extensive necrosis, apoptosis and macro- and micro-steatosis, with DENV-2 antigen-positive Kuppfer cells and hepatocytes. Their infections were confirmed by DENV-2 isolations from their lungs, spleens and livers. These findings accord with those reported in fatal human "severe dengue" cases. This DENV-2 AER/AED was blocked by high concentrations of only the NG-C NS1 glycoprotein. These results imply a potential hazard of DENV NS1 glycoprotein-based vaccines, particularly against DENV strains that contain multiple mutations or genetic recombination within or between their DENV E and NS1 glycoprotein-encoding genes. The model provides potential for assessing DENV strain pathogenicity and anti-DENV therapies in normal mice.

Insulin-like growth factor 2 receptor is an IFNgamma-inducible microglial protein that facilitates intracellular HIV replication: implications for HIV-induced neurocognitive disorders

Insulin-like growth factor 2 receptor (IGF2R), also known as cation-independent mannose 6-phosphate (M6P) receptor, is a transmembrane glycoprotein localized in the trans-Golgi region and is involved in targeting both M6P-bearing enzymes and IGF2 to the lysosomal compartment. During development, IGF2R plays a crucial role in removing excess growth factors from both tissue and blood. Due to the perinatal lethality of the global Igf2r knockout, the function of IGF2R in adults, particularly in the CNS, is not known. We made a novel observation that IGF2R is highly expressed in microglial nodules in human brains with HIV encephalitis. In vitro, microglial IGF2R expression was uniquely enhanced by IFNγ among the several cytokines and TLR ligands examined. Furthermore, in several in vitro models of HIV infection, including human and murine microglia, macrophages, and nonmacrophage cells, IGF2R is repeatedly shown to be a positive regulator of HIV infection. IGF2R RNAi also down-regulated the production of the IP-10 chemokine in HIV-infected human microglia. Injection of VSVg env HIV into mouse brain induced HIV p24 expression in neurons, the only cell type normally expressing IGF2R in the adult brain. Our results demonstrate a novel role for IGF2R as an inducible microglial protein involved in regulation of HIV and chemokine expression. Mice with the Csf1r- driven Igf2r knockout should be useful for the investigation of macrophage-specific IGF2R function.

Involvement of Fc receptors in disorders of the central nervous system

Immunoglobulins are proteins with a highly variable antigen-binding domain and a constant region (Fc domain) that binds to a cell surface receptor (FcR). Activation of FcRs in immune cells (lymphocytes, macrophages, and mast cells) triggers effector responses including cytokine production, phagocytosis, and degranulation. In addition to their roles in normal responses to infection or tissue injury, and in immune-related diseases, FcRs are increasingly recognized for their involvement in neurological disorders. One or more FcRs are expressed in microglia, astrocytes, oligodendrocytes, and neurons. Aberrant activation of FcRs in such neural cells may contribute to the pathogenesis of major neurodegenerative conditions including Alzheimer's disease, Parkinson's disease, ischemic stroke, and multiple sclerosis. On the other hand, FcRs may play beneficial roles in counteracting pathological processes; for e.g., FcRs may facilitate removal of amyloid peptides from the brain and so protect against Alzheimer's disease. Knowledge of the functions of FcRs in the nervous system in health and disease is leading to novel preventative and therapeutic strategies for stroke, Alzheimer's disease, and other neurological disorders.

Alterations of Fc gamma receptor I and Toll-like receptor 4 mediate the antiinflammatory actions of microglia and astrocytes after adrenaline-induced blood-brain barrier opening in rats

Blood-brain barrier (BBB) opening occurs under many physiological and pathological conditions. BBB opening will lead to the leakage of large circulating molecules into the brain parenchyma. These invasive molecules will induce immune responses. Microglia and astrocytes are the two major cell types responsible for immune responses in the brain, and Fc gamma receptor I (FcgammaRI) and Toll-like receptor 4 (TLR4) are the two important receptors mediating these processes. Data suggest that activation of the FcgammaRI pathway mediates antiinflammatory processes, whereas activation of TLR4 pathway leads to proinflammatory activities. In the present study, we tested the hypothesis that BBB opening could lead to alterations in FcgammaRI and TLR4 pathways in microglia and astrocytes, thus limiting excessive inflammation in the brain. The transient BBB opening was induced by adrenaline injection through a caudal vein in Sprague-Dawley rats. We found that the FcgammaRI pathway was significantly activated in both microglia and astrocytes, as exhibited by the up-regulation of FcgammaRI and its key downstream molecule Syk, as well as the increased production of the effector cytokines, interleukin (IL)-10 and IL-4. Interestingly, after transient BBB opening, TLR4 expression was also increased. However, the expression of MyD88, the central adapter of the TLR4 pathway, was significantly inhibited, with decreased production of the effector cytokines IL-12a and IL-1beta. These results indicate that, after transient BBB opening, FcgammaRI-mediated antiinflammatory processes were activated, whereas TLR4-mediated proinflammatory activities were inhibited in microglia and astrocytes. This may represent an important neuroprotective mechanism of microglia and astrocytes that limits excessive inflammation after BBB opening.

Fc gamma receptors regulate immune activation and susceptibility during Mycobacterium tuberculosis infection

The critical role of cellular immunity during tuberculosis (TB) has been extensively studied, but the impact of Abs upon this infection remains poorly defined. Previously, we demonstrated that B cells are required for optimal protection in Mycobacterium tuberculosis-infected mice. FcgammaR modulate immunity by engaging Igs produced by B cells. We report that C57BL/6 mice deficient in inhibitory FcgammaRIIB (RIIB-/-) manifested enhanced mycobacterial containment and diminished immunopathology compared with wild-type controls. These findings corresponded with enhanced pulmonary Th1 responses, evidenced by increased IFN-gamma-producing CD4+ T cells, and elevated expression of MHC class II and costimulatory molecules B7-1 and B7-2 in the lungs. Upon M. tuberculosis infection and immune complex engagement, RIIB-/- macrophages produced more of the p40 component of the Th1-promoting cytokine IL-12. These data strongly suggest that FcgammaRIIB engagement can dampen the TB Th1 response by attenuating IL-12p40 production or activation of APCs. Conversely, C57BL/6 mice lacking the gamma-chain shared by activating FcgammaR had enhanced susceptibility and exacerbated immunopathology upon M. tuberculosis challenge, associated with increased production of the immunosuppressive cytokine IL-10. Thus, engagement of distinct FcgammaR can divergently affect cytokine production and susceptibility during M. tuberculosis infection.

Global changes in optic nerve head gene expression after exposure to elevated intraocular pressure in a rat glaucoma model

PURPOSE

In glaucoma, the optic nerve head (ONH) is the likely site of initial injury and elevated intraocular pressure (IOP) is the best-known risk factor. This study determines global gene expression changes in the pressure-injured ONH.

METHODS

Unilateral sustained IOP elevation (glaucoma, n = 46) or optic nerve transection (n = 10) was produced in rats. ONHs were removed, and the retrobulbar optic nerves were graded for degeneration. Gene expression in the glaucomatous ONH with extensive injury was compared with that in the fellow ONH (n = 6/group), by using cDNA microarrays. Data from 12 arrays were normalized, significant differences in gene expression determined, and significantly affected gene classes identified. For the remaining ONH, grouped by experimental condition and degree of injury, quantitative reverse transcriptase-PCR (qPCR) and ANOVA were used to compare selected message levels.

RESULTS

Microarray analysis identified more than 2000 significantly regulated genes. For 225 of these genes, the changes were greater than twofold. The most significantly affected gene classes were cell proliferation, immune response, lysosome, cytoskeleton, extracellular matrix, and ribosome. A 2.7-fold increase in ONH cellularity confirmed glaucoma model cell proliferation. By qPCR, increases in levels of periostin, collagen VI, and transforming growth factor beta1 were linearly correlated to the degree of IOP-induced injury. For cyclinD1, fibulin 2, tenascin C, TIMP1, and aquaporin-4, correlations were significantly nonlinear, displaying maximum change with focal injury.

CONCLUSIONS

In the ONH, pressure-induced injury results in cell proliferation and dramatically altered gene expression. For specific genes, expression levels were most altered by focal injury, suggesting that further array studies may identify initial, and potentially injurious, altered processes.

Immune complexes alter cerebral microvessel permeability: roles of complement and leukocyte adhesion

Immune complexes (ICs) are potent inflammatory mediators in peripheral tissues. However, very few studies have examined the ability of ICs to induce inflammatory responses in the brain. Therefore, using preformed ICs or the reverse passive Arthus (RPA) model to localize ICs to the pial microvasculature of mice, we aimed to investigate the ability of ICs to induce an inflammatory response in the cerebral (pial) microvasculature. Application of preformed ICs immediately increased pial microvascular permeability, with a minimal change in leukocyte adhesion in pial postcapillary venules. In contrast, initiation of the RPA response in the pial microvasculature induced changes in cerebral microvascular permeability and increased leukocyte adhesion in pial postcapillary venules. The RPA response induced deposition of C3 in perivascular regions adjacent to sites of IC formation. Depletion of C3 abrogated RPA-induced microvascular permeability and leukocyte adhesion, indicating that the complement pathway was critical for this response. Inhibition of leukocyte adhesion via CD18 blockade also reduced IC-induced microvascular permeability. However, this did not require intercellular adhesion molecule-1, inasmuch as blockade of intercellular adhesion molecule-1 did not alter RPA-induced microvascular permeability and adhesion. These findings demonstrate that ICs are capable of rapidly inducing inflammatory responses in the cerebral microvasculature, with the complement pathway and leukocyte recruitment playing critical roles in microvascular dysfunction.

Humoral immunity in brain aging and Alzheimer's disease

Although the contribution of inflammatory processes in the etiology of late-onset Alzheimer's disease (AD) has been suspected for years, most studies were confined to the analysis of cell-mediated immunological reactions thought to represent an epiphenomenon of AD lesion development. Based on the traditional view of the "immunological privilege" of the brain, which excludes a direct access of human immunoglobulins (Ig) to the central nervous system under normal conditions, little attention has been paid to a possible role of humoral immunity in AD pathogenesis. In the first part of this review, we summarize evidences for a blood-brain barrier (BBB) dysfunction in this disorder and critically comment on earlier observations supporting the presence of anti-brain autoantibodies and immunoglobulins (Ig) in AD brains. Current concepts regarding the Ig turnover in the central nervous system and the mechanisms of glial and neuronal Fc receptors activation are also discussed. In the second part, we present new ex vivo and in vitro data suggesting that human immunoglobulins can interact with tau protein and alter both the dynamics and structural organization of microtubules. Subsequent experiments needed to test this new working hypothesis are addressed at the end of the review.

Melanization of Cryptococcus neoformans affects lung inflammatory responses during cryptococcal infection

The production of melanin pigments is associated with virulence for many microbes. Melanin is believed to contribute to microbial virulence by protecting microbial cells from oxidative attack during infection. However, there is also evidence from various systems that melanins have immunomodulatory properties, which conceivably could contribute to virulence by altering immune responses. To investigate the effect of melanin on the immune response, we compared the murine pulmonary responses to infection with melanized and nonmelanized Cryptococcus neoformans cells. Infection with melanized cells resulted in a greater fungal burden during the early stages of infection and was associated with higher levels of interleukin-4 and MCP-1 and greater numbers of infiltrating leukocytes. Infection with laccase-positive (melanotic) C. neoformans cells also elicited higher MCP-1 levels and more infiltrating leukocytes than did infection with laccase-negative cells. Melanization interfered with phagocytosis in vivo for encapsulated C. neoformans but not for nonencapsulated cells. The results provide strong evidence that cryptococcal melanization can influence the immune response to infection and suggest that immunomodulation is an additional mechanism by which the pigment contributes to virulence.

The FcRγ Chain Is Not Essential for Induction of Experimental Allergic Encephalomyelitis (EAE) or Anti-Myelin Antibody-Mediated Exacerbation of EAE

Macrophages are considered essential mediators in multiple sclerosis (MS) pathogenesis, presumably through myelin phagocytosis and release of inflammatory mediators. Macrophages and microglia express activating Fcgamma receptors (FcgammaRI and FcgammaRIII), which depend on the FcRgamma chain for surface expression and signaling. In MS lesions, crosslinking of FcgammaR by immunoglobulins (IgG) directed against myelin may enhance myelin phagocytosis and inflammation. We studied the role of FcgammaR and anti-myelin antibodies in MOG35-55-induced experimental allergic encephalomyelitis (EAE) in C57BL/6 mice, a model of MS-like disease. Incidence and severity of EAE were similar in FcRy chain-/- (FcRgamma-/-) and wild-type (wt) mice, albeit with delayed onset in FcRgamma-/- mice. This demonstrates that the FcRy chain is not essential for induction of EAE, but that FcRgamma signaling may contribute to the preclinical phase. The role of FcgammaR in antibody-mediated demyelination was addressed by injection of anti-myelin antibodies (Z12 mAb) at onset of MOG35-55-induced EAE. Injection of Z12 mAb rapidly reduced survival time in both wt and FcRgamma-/- mice, demonstrating that antibody-mediated exacerbation of EAE is independent of the FcRgamma chain. Interestingly, Z12-induced exacerbation of inflammation and demyelination persisted longer in wt than FcRgamma-/- mice, suggesting that IgG-FcgammaR interactions may contribute to a sustained pathologic effect of anti-myelin antibodies in the CNS.

Pigment epithelium-derived factor induces the production of chemokines by rat microglia

Many studies have shown that pigment epithelium-derived factor (PEDF) has neurotrophic effects on retinal cells and hippocampal, spinal cord, and cerebellar granule cell neurons, but much less work has examined the effects of PEDF on glia. In this study, we show that PEDF changes microglial morphology within 1 h of exposure, to a more deactivated form, while having no effect on the expression of such activation markers as OX-42 and ED-1. In contrast, urea activates acid phosphatase, and PEDF blocks that activation. PEDF also activates NFkappaB, accompanied by the induction of mRNAs and proteins for the chemokines macrophage inflammatory protein-1alpha (MIP-1alpha, MIP-2, and MIP-3alpha. All the chemokines stimulate acid phosphatase activity, and high doses of MIP-2 and MIP-3alpha), alter the morphology of the microglia at 1 h after treatment. These results suggest that the use of PEDF for clinical treatments, such as for retinal neovascularization, brain injury, or ischemia, should be undertaken with caution because of the possibility of induction of inflammation caused by microglial or other immune cell migration in response to the chemokines induced by PEDF.

Differential gene expression modulated by the cytoplasmic domain of Fc gamma RIa (CD64) alpha-chain

The cytoplasmic domain (CY) of the ligand-binding alpha-chain of the gamma-chain-associated FcRs can modulate receptor function such as phagocytosis, endocytosis, and intracellular trafficking of receptor-Ag complexes. To assess the potential role of the CY domain of human FcgammaRIa (CD64) alpha-chain in the transcriptional regulation of receptor-induced gene expression, we developed stably transfected murine macrophage cell lines expressing a full-length or a CY deletion mutant (tail-less) of human FcgammaRIa to analyze gene expression in response to receptor-specific cross-linking. Using the Affymetrix murine genome U74Av2 GeneChip array, we observed >100 candidate genes having > or =2-fold difference expression at 1.5 and 3 h after stimulation. Focusing on several immunologically related genes, we confirmed differential expression of M-CSF, macrophage inhibitory cytokine-1, leukocyte-specific protein 1, MIP-2, and IL-1R antagonist by RT-PCR and RNase protection assays. Analysis of mRNA stability indicated that the differential regulation of gene expression by the CY of the CD64 alpha-chain is at the level of gene transcription. Our results indicate that the CY of the CD64 alpha-chain modulates transcriptional activity induced by receptor-specific engagement in macrophages and provides a framework for understanding distinct expression profiles elicited by different Fc gamma-chain-associated receptors.

Role of microglia in central nervous system infections

The nature of microglia fascinated many prominent researchers in the 19th and early 20th centuries, and in a classic treatise in 1932, Pio del Rio-Hortega formulated a number of concepts regarding the function of these resident macrophages of the brain parenchyma that remain relevant to this day. However, a renaissance of interest in microglia occurred toward the end of the 20th century, fueled by the recognition of their role in neuropathogenesis of infectious agents, such as human immunodeficiency virus type 1, and by what appears to be their participation in other neurodegenerative and neuroinflammatory disorders. During the same period, insights into the physiological and pathological properties of microglia were gained from in vivo and in vitro studies of neurotropic viruses, bacteria, fungi, parasites, and prions, which are reviewed in this article. New concepts that have emerged from these studies include the importance of cytokines and chemokines produced by activated microglia in neurodegenerative and neuroprotective processes and the elegant but astonishingly complex interactions between microglia, astrocytes, lymphocytes, and neurons that underlie these processes. It is proposed that an enhanced understanding of microglia will yield improved therapies of central nervous system infections, since such therapies are, by and large, sorely needed.

Gene expression differences of regenerating rat liver in a short interval successive partial hepatectomy

AIM: To identify the genes expressed differentially in the regenerating rat liver in a short interval successive partial hepatectomy (SISPH), and to analyze their expression profiles.

METHODS: Five hundred and fifty-one elements selected from subtractive cDNA libraries were conformed to a cDNA microarray (cDNA chip). An extensive gene expression analysis following 0-36-72-96-144 h SISPH was performed by microarray.

RESULTS: Two hundred and sixteen elements were identified either up- or down-regulated more than 2-fold at one or more time points of SISPH. By cluster analysis and generalization analysis, 8 kinds of ramose gene expression clusters were generated in the SISPH. Of the 216 elements, 111 were up-regulated and 105 down-regulated. Except 99 unreported genes, 117 reported genes were categorized into 22 groups based on their biological functions. Comparison of the gene expression in SISPH with that after partial hepatectomy (PH) disclosed that 56 genes were specially altered in SISPH, and 160 genes were simultaneously up-regulated or down-regulated in SISPH and after PH, but in various amount and at different time points.

CONCLUSION: Genes expressed consistently are far less than that intermittently; the genes strikingly increased are much less than that increased only 2-5 fold; the expression trends of most genes in SISPH and in PH are similar, but the expression of 56 genes is specifically altered in SISPH. Microarray combined with suppressive subtractive hybridization can in a large scale effectively identify the genes related to liver regeneration.

Gene expression difference in regenerating rat liver after 0-36-40-44h short interval successive partial hepatectomy

AIM: To identify genes related to rat liver regeneration (LR) after 0-36-40-44h short interval successive partial hepatectomy (SISPH) and to analyze their action and expression profile in LR.

METHODS: A cDNA microarray containing 551 elements (liver chip) was made to analyze extensively expression changes of them in 0-36-40-44h SISPH, which were selected from subtractive cDNA libraries of the LR. Cluster analysis of these gene expression profile was performed by Genemath.

RESULTS: Among the selected 551 cDNA, 157 were up- ordown-regulated more than twofold at one or more time points. Of the 157 elements, 86 were up-regulated and 71 down-regulated, and 70 were not reported and 87 were reported, which had not been previously reported to be involved in LR. By cluster analysis and generalization analysis, 6 distinct temporal induction or suppression patterns showed that immediate induction, intermediate induction, late induction, immediate suppression, intermediate suppression, and late suppression. Comparison of the gene expression in SISPH with after PH found that 38 genes were specially altered in SISPH, and the expression trends for other 119 genes were similar between SISPH and PH, except of the various abundance at the different time points.

CONCLUSION: In 0-36-40-44h SISPH, the numbers of the up-regulated and down-regulated genes show no apparent difference. The genes expressed lately are more than that immediately, and much more than that intermediately. The genes expressed abundantly are much less than that increased 2-5 folds.

Fcγ receptor signaling in primary human microglia: differential roles of PI-3K and Ras/ERK MAPK pathways in phagocytosis and chemokine induction

Cryptococcus neoformans monoclonal antibody immune complex (IC) induces beta-chemokines and phagocytosis in primary human microglia via activation of Fc receptor for immunoglobulin G (FcgammaR). In this report, we investigated microglial FcgammaR signal-transduction pathways by using adenoviral-mediated gene transfer and specific inhibitors of cell-signaling pathways. We found that Src inhibitor PP2 and Syk inhibitor piceatannol inhibited phagocytosis, macrophage-inflammatory protein-1alpha (MIP-1alpha) release, as well as phosphorylation of extracellular-regulated kinase (ERK) and Akt, consistent with Src/Syk involvement early in FcgammaR signaling. Constitutively active mitogen-activated protein kinase kinase (MEK) induced MIP-1alpha, and Ras dominant-negative (DN) inhibited IC-induced ERK phosphorylation and MIP-1alpha production. These results suggest that the Ras/MEK/ERK pathway is necessary and sufficient in IC-induced MIP-1alpha expression. Neither Ras DN nor the MEK inhibitor U0126 inhibited phagocytosis. In contrast, phosphatidylinositol-3 kinase (PI-3K) inhibitors Wortmannin and LY294002 inhibited phagocytosis without affecting ERK phosphorylation or MIP-1alpha production. Conversely, Ras DN or U0126 did not affect Akt phosphorylation. Together, these results demonstrate distinct roles played by the PI-3K and Ras/MEK/ERK pathways in phagocytosis and MIP-1alpha induction, respectively. Our results demonstrating activation of functionally distinct pathways following microglial FcgammaR engagement may have implications for human central nervous system diseases.

Microglia from mice transgenic for a provirus encoding a monocyte-tropic HIV type 1 isolate produce infectious virus and display in vitro and in vivo upregulation of lipopolysaccharide-induced chemokine gene expression

A large body of evidence has indicated that microglia are the predominant cellular location for HIV-1 in the brains of HIV-1-infected individuals and play a direct role in the development of HIV-1-associated dementia (HAD). Therefore, investigation of the mechanism by which HIV-1-infected microglia contribute to the development of HIV-associated dementia should be facilitated by the creation of a mouse model wherein microglia carry replication-competent HIV-1. To circumvent the inability of HIV-1 to infect mouse cells, we developed a mouse line that is transgenic for a full-length proviral clone of a monocyte-tropic HIV-1 isolate, HIV-1(JR-CSF) (JR-CSF mice), whose T cells and monocytes produce infectious HIV-1. We detected expression of the long terminal repeat-regulated proviral transgene in the microglia of these transgenic mice and demonstrated that it was increased by in vitro and in vivo stimulation with lipopolysaccharide. Furthermore, microglia isolated from JR-CSF mouse brains produced HIV-1 that was infectious in vitro and in vivo. We examined the effect that carriage of the HIV-1 provirus had on chemokine gene regulation in the brains of these mice and demonstrated that MCP-1 gene expression by JR-CSF mouse microglia and brains was more responsive to in vitro and in vivo stimulation with lipopolysaccharide than were microglia and brains from control mice. Thus, this study indicates that the JR-CSF mice may represent a new mouse model to study the effect of HIV-1 replication on microglia function and its contribution to HIV-1-associated neurological disease.

The origin and maintenance of virulence for the human pathogenic fungus Cryptococcus neoformans

The origin of virulence in environmental fungi that have no requirement for animal hosts in their life cycle is enigmatic. Cryptococcus neoformans is a human pathogenic fungus with virulence factors for mammalian pathogenesis that also contribute to environmental survival. C. neoformans virulence may originate from selection pressures imposed by environmental predators.

Phagocytic activity and monocyte chemotactic protein expression by pulmonary macrophages in persistent pulmonary cryptococcosis

The mechanisms by which Cryptococcus neoformans persists in an immunocompetent host are not well understood. Using a rat model of persistent infection, we investigated the ability of pulmonary macrophages (PuM) to phagocytize C. neoformans and produce monocyte chemotactic protein 1 (MCP-1) as a function of the length of time of infection and opsonin. The ability of macrophages to affect serum-mediated phagocytosis varied over the course of infection and was dependent on CD11b/c and CD18 expression. Infection resulted in increased MCP-1 levels within the lung, though the actual amounts varied over the course of infection. Immunohistochemical studies localized MCP-1 expression to macrophages and epithelioid cells. Enhanced production of MCP-1 by PuM from infected rats was confirmed by ex vivo studies. Induction of MCP-1 following serum-mediated phagocytosis was observed for PuM from both infected and noninfected rats and depended on the interaction of C. neoformans with CD11b/c and CD18. Specific antibody was more efficient than serum in promoting phagocytosis and consistently elicited more MCP-1. The relative amount of MCP-1 produced in association with phagocytosis was similar for PuM at all lengths of time of infection. Decreased MCP-1 production was observed for PuM obtained from older rats, including long-term (8 to 10 months)-infected and age-matched controls, suggesting that aging may affect the production of MCP-1 by PuM in response to cryptococcal infection. In summary, our results show that macrophages are an important source of MCP-1 during pulmonary cryptococcosis and that MCP-1 production is actively regulated during infection. Furthermore, we find that phagocytosis of C. neoformans can serve as an important stimulus for MCP-1 production by PuM, though the efficiency of this process is dependent on the opsonin type and may be affected by aging.