Toll-like receptor 4 and CD11b expressed on microglia coordinate eradication of Candida albicans cerebral mycosis

The fungal pathogen Candida albicans is linked to chronic brain diseases such as Alzheimer's disease (AD), but the molecular basis of brain anti-Candida immunity remains unknown. We show that C. albicans enters the mouse brain from the blood and induces two neuroimmune sensing mechanisms involving secreted aspartic proteinases (Saps) and candidalysin. Saps disrupt tight junction proteins of the blood-brain barrier (BBB) to permit fungal brain invasion. Saps also hydrolyze amyloid precursor protein (APP) into amyloid β (Aβ)-like peptides that bind to Toll-like receptor 4 (TLR4) and promote fungal killing in vitro while candidalysin engages the integrin CD11b (Mac-1) on microglia. Recognition of Aβ-like peptides and candidalysin promotes fungal clearance from the brain, and disruption of candidalysin recognition through CD11b markedly prolongs C. albicans cerebral mycosis. Thus, C. albicans is cleared from the brain through innate immune mechanisms involving Saps, Aβ, candidalysin, and CD11b.

STAT6 Blockade Abrogates Aspergillus-Induced Eosinophilic Chronic Rhinosinusitis and Asthma, A Model of Unified Airway Disease

Unified airway disease, including concurrent asthma and chronic rhinosinusitis (CRS), is a common, but poorly understood disorder with no curative treatment options. To establish a murine model of chronic unified eosinophilic airway inflammation, mice were challenged with Aspergillus niger, and sinonasal mucosa and lung tissue were evaluated by immunohistochemistry, flow cytometry, and gene expression. Inhalation of A niger conidia resulted in a Th2-biased lung and sinus inflammation that typifies allergic asthma and CRS. Gene network and pathway analysis correlated with human disease with upregulation of not only the JAK-STAT and helper T-cell pathways, but also less expected pathways governing the spliceosome, osteoclast differentiation, and coagulation pathways. Utilizing a specific inhibitor and gene-deficient mice, we demonstrate that STAT6 is required for mycosis-induced sinus inflammation. These findings confirm the relevance of this new model and portend future studies that further extend our understanding of the immunopathologic basis of airway mycosis and unified airway disease.

Novel acute hypersensitivity pneumonitis model induced by airway mycosis and high dose lipopolysaccharide

BACKGROUND

Inhalation of fungal spores is a strong risk factor for severe asthma and experimentally leads to development of airway mycosis and asthma-like disease in mice. However, in addition to fungal spores, humans are simultaneously exposed to other inflammatory agents such as lipopolysaccharide (LPS), with uncertain relevance to disease expression. To determine how high dose inhalation of LPS influences the expression of allergic airway disease induced by the allergenic mold Aspergillus niger (A. niger).

METHODS

C57BL/6J mice were intranasally challenged with the viable spores of A. niger with and without 1 μg of LPS over two weeks. Changes in airway hyperreactivity, airway and lung inflammatory cell recruitment, antigen-specific immunoglobulins, and histopathology were determined.

RESULTS

In comparison to mice challenged only with A. niger, addition of LPS (1 μg) to A. niger abrogated airway hyperresponsiveness and strongly attenuated airway eosinophilia, PAS+ goblet cells and TH2 responses while enhancing TH1 and TH17 cell recruitment to lung. Addition of LPS resulted in more severe, diffuse lung inflammation with scattered, loosely-formed parenchymal granulomas, but failed to alter fungus-induced IgE and IgG antibodies.

CONCLUSIONS

In contrast to the strongly allergic lung phenotype induced by fungal spores alone, addition of a relatively high dose of LPS abrogates asthma-like features, replacing them with a phenotype more consistent with acute hypersensitivity pneumonitis (HP). These findings extend the already established link between airway mycosis and asthma to HP and describe a robust model for further dissecting the pathophysiology of HP.

Expression of gamma-aminobutyric acid immunoreactivity in reactive astrocytes after ischemia-induced injury in the adult forebrain

Transient ischemia induces an increase in glial fibrillary acidic protein (GFAP) immunoreactivity which can be detected in specific forebrain regions of the adult gerbil as early as day 2, becomes prominent by day 4-7 and persists for at least 3 months. These forebrain areas include layers 2/3 of the somatosensory and auditory cortices, the CA1 and CA4 sectors of the hippocampus, the dorsolateral region of the striatum, and the dorsolateral subregion of the medial septal nucleus. In addition, astrocytes in the ischemically lesioned areas stain with gamma aminobutyric acid (GABA) antiserum. These GABA-immunoreactive astrocytes are not found in non-damaged areas. The time-course of expression of GABA immunoreactivity is similar to that of GFAP immunoreactivity. Using a double immunofluorescent staining method, reactive astrocytes which express GABA immunoreactivity were also found to immunostain with either GFAP or vimentin. On the other hand, astrocytes were not found to be immunoreactive with antibodies to glutamic acid decarboxylase or glutamate. Our present finding demonstrates, in an in vivo model, an aberrant expression of GABA immunoreactivity by astrocytes which is not observed in non-ischemic adult animals.

Ischemic damage in the striatum of adult gerbils: relative sparing of somatostatinergic and cholinergic interneurons contrasts with loss of efferent neurons

The pattern of ischemia-induced cell death was examined with histochemical methods in the striatum of adult gerbils 4 and 7 days after transient forebrain ischemia. The results showed a massive loss of immunoreactivity to enkephalin and tachykinins, peptides present in striatal efferent neurons. In contrast, neurons expressing acetylcholinesterase activity, or choline acetyltransferase immunoreactivity, as well as neurons immunoreactive for somatostatin, were relatively preserved in areas of severe neuronal loss. The selective vulnerability of subpopulations of striatal neurons to transient ischemia in the adult is similar to that observed in the neonate and after local injections of agonists of N-methyl-D-aspartate receptors, but not of agonists of other glutamate receptor subtypes. It also presents striking similarities to the pattern of neuronal death observed in Huntington's disease. The results further support a role for overstimulation of a subtype of excitatory amino acid receptor in ischemia-induced cell death and show that the selective sparing of subpopulations of striatal interneurons after ischemic injury is not related to immaturity of these neurons but also occurs in the adult.

Electron microscopic study of the gerbil dentate gyrus after transient forebrain ischemia

Silver impregnation performed 1-2 days after transient forebrain ischemia in the Mongolian gerbil demonstrated terminal-like granular deposits in the outer two-thirds of the hippocampal dentate molecular layer (perforant path terminal zone), even though neither the cell bodies of origin of the perforant path nor the dentate granule cells were destroyed. Electron microscopic studies of the dentate gyrus were performed in an effort to discover the identity of these degenerating structures. Electron microscopy revealed that the granular silver deposits corresponded to electron-dense profiles. Many of these were degenerating boutons and some were degenerating postsynaptic dendritic fragments, but most of them could not be identified with certainty. Electron-dense profiles were less numerous than expected from the density of granular silver deposits. These structures were probably the degenerating axons, axon terminals and dendrites of CA4 neurons. The granular silver deposits and electron-dense boutons observed in the inner third of the dentate molecular layer 5 days after transient ischemia can probably be explained by the ischemia-induced degeneration of CA4 mossy cells, which give rise to the dentate associational-commissural projection. Finally, most mossy fiber boutons in area CA4 and some boutons in the molecular layer appeared watery and enlarged on postischemia days 1 and 2. Mossy fiber boutons with this ultrastructural appearance have previously been observed in seizure-prone animals and in animals undergoing convulsant-induced seizures. Although no postischemic seizures occur under the conditions of this study, these findings support the idea that excitatory pathways become hyperactive after transient ischemia.

Selective neocortical and thalamic cell death in the gerbil after transient ischemia

In animal models of transients ischemia, selective vulnerability and delayed neuronal death in the hippocampus have been extensively described. However, little is known about selective damage in the neocortex and the thalamus, even though deficits in sensorimotor function are common in humans surviving hypoxic/ischemic episodes. This study investigated the neurodegenerative effects of transient ischemia in the gerbil neocortex and thalamus with use of Cresyl Violet and silver impregnation staining methods. In addition, immunohistochemistry of an astrocyte-associated protein, glial fibrillary acidic protein, was used to assess the astrocytic response to ischemia. Pyramidal cells in layers 3 and 6 of somatosensory and auditory cortex were exceptionally sensitive to ischemia, whereas the neurons in layers 2, 4 and 5 were more resistant to ischemia. More pyramidal cells were killed in layer 3 than in layer 6. This bilaminar pattern of neuronal death developed after periods of ischemia ranging from 3 to 10 min and was identifiable at post-ischemic survival times of 6 h to one month. Somatodendritic argyrophilia in the neocortex was identified as early as 6-12 h after 5 min of ischemia. The greatest number of degenerating cortical neurons were stained two to four days after ischemia. With 10 min of ischemia, argyrophilic neurites and neurons were also found as early as 8 h after the occlusion. The most extensive damage was noted in the ventroposterior nucleus, the medial geniculate nucleus, and the intralaminar nuclei two to four days after ischemia. Thus, selective vulnerability and delayed neuronal death are evident in both the neocortex and the thalamus after transient ischemia. These regions need to be examined when considering the efficacy of potential neuroprotective drugs.