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The pathogenesis of viral infections involves an immune response by cytokines, causing a deleterious effect on organ function, in addition to tissue destruction due to viral replication. Clinical symptoms and laboratory findings of the human coronavirus disease COVID-19, caused by the novel coronavirus SARS CoV-2, indicate cytokine involvement. Our laboratory showed that an experimental murine coronavirus (MHV-A59) can be transmitted into the brain by intranasal or intracerebral exposure and that neurovirulence is mediated by cytokine secretion. In this study we investigated which cells in the brain produce cytokines, thus functioning as the brain's innate immune system. Using tissue cultures of microglia, and clonal populations of astrocytes, we found that microglia and type I astrocytes (but not types II and III), produced pro-inflammatory cytokines in response to MHV-A59 infection. A molecularly closely related, non-encephalitic strain of the virus (MHV-2) caused in vitro infection, but without cytokine induction. Furthermore, immunofluorescence and immunohistochemistry revealed that type I astrocytes and microglia have perivascular foot processes necessary for the formation of the perivascular glymphatic system, the anatomical site of the brain's innate immune system. Cytokine secretion by type I astrocytes and microglia, as part of the brain's glymphatic and innate immune system, contributes to the pathogenesis of an encephalitic coronavirus infection, and indicates the rationale for anti-cytokine therapies for COVID-19., Highlights • Cytokine induction mediates the neurologic pathogenesis of coronavirus infection. • Type I astrocytes and microglia send foot-processes around blood vessels in the brain, forming the glymphatic system, the site for the brain's innate immune system. • The brain's innate immune system functions during coronavirus infection by the induction of pro-inflammatory cytokines. • This experimental coronavirus model system sheds light on the neurologic manifestations of the human coronavirus disease COVID-19.

Peripheral neuropathy, white matter abnormalities, and cardiomyopathy are associated findings with merosin-deficient congenital muscular dystrophy. Although characterization of the neuropathy with nerve conduction studies has been well documented, limited research has been able to correlate histopathology with nerve biopsy in humans. Our understanding of the mechanism, described as a demyelinating neuropathy, is mainly derived from mouse model studies. We report a 23-year-old male who succumbed to respiratory failure and ultimately cardiac arrhythmia in the setting of an uncharacterized end stage progressive muscular disease complicated by cardiomyopathy and severe scoliosis. Autopsy revealed extensive muscular atrophy and replacement by fibroadipose tissue throughout the skeletal muscle and myocardium. Immunohistochemical analysis of the muscle biopsy showed a complete loss of merosin. Thus, the cause for both his muscular disease and demyelinating neuropathy was established with the diagnosis of merosin-deficient muscular dystrophy. Nerve biopsy obtained from the cauda equina showed clear evidence of segmental demyelination and remyelination, providing a better understanding of the proximal peripheral nerve histopathological changes in this disease entity.

Within the differential diagnosis of patients presenting with sellar or suprasellar lesions is Langerhans cell histiocytosis (LCH). CD1a staining is frequently used to identify the presence of an abnormal proliferation of Langerhans cells on histological sections and contributes to the diagnosis of LCH. Here, we report that the MTB-1 monoclonal antibody against the CD1a antigen reacts to native adenohypophyseal epithelial cells. We show that immunohistochemistry for CD1a exhibits strong positivity in all autopsy and surgically resected non-neoplastic adenohypophysis tested. Thus, CD1a positivity by itself should be interpreted with caution, and we recommend the routine use of a panel of stains including CD1a, Langerin, and synaptophysin in conjunction with morphological analysis before a diagnosis of LCH is rendered. In addition, we find that pituitary adenomas fail to stain for CD1a prompting consideration of the utility of this stain as a marker for non-neoplastic gland.

Mouse hepatitis virus causes a chronic demyelinating disease in C57BL/6 mice. While early studies suggested demyelination is due to direct cytolytic effects of virus on oligodendrocytes, there is increasing evidence for the involvement of the immune system in the mechanism of demyelination. In this study we have asked whether demyelination can occur in the absence of functional MHC class I expression and CD8+ T cells. We infected transgenic mice lacking expression of beta 2 microglobulin (beta 2 M -/- mice) with MHV-A59. In beta 2M-/- mice, virus was much more lethal than in either of the parental strains used to produce the mice; furthermore, while clearance from the CNS did occur in beta 2M-/- mice, it was slower than in C57BL/6 mice. This is consistent with the importance of CD8+ cells in viral clearance. Because of the increased sensitivity of the beta 2M-/- mice to infection, only low levels of virus could be used to evaluate chronic disease. Even at these low levels, demyelination did occur in some animals. To compare infection in beta 2M-/- and C57BL/6 mice we used a higher dose of an attenuated variant of MHV-A59, C12. The attenuated variant induced less demyelination in C57BL/6 mice compared to wild type A59, but the levels observed were not significantly different from those seen in beta 2M-/- mice. Thus, MHV-induced demyelination can occur in some animals in the absence of MHC class I and CD8+ cells.

Infection of mice with mouse hepatitis virus (MHV) strain A59 results in acute encephalitis, hepatitis, and chronic demyelinating disease. T lymphocytes play an important role in MHV infection, and costimulatory signals are an important component of T cell function. To elucidate the role of the main costimulatory molecule, CD28, in MHV pathogenesis and demyelination, we examined the kinetics of MHV-A59 infection in CD28 knockout mice. MHV-A59-infected CD28 knockout mice developed acute encephalitis and hepatitis, and the same degree of chronic demyelination as normal C57Bl/6 (B6) mice. Thus, CD28, the costimulatory T cell molecule, is not required for MHV infection and MHV-induced demyelination.

The Golgi apparatus-complex (GA), is a key organelle involved in several posttranslational modifications of polypeptides destined for lysosomes, plasma membranes and secretion. As reported from this laboratory, certain astrocytes in rat brain contain cisternae of the GA not only in perikarya, but also in processes. In order to further investigate which type of astrocytes contain GA in processes we conducted the present study using primary cultures of rat astrocytes and organelle specific antibodies against the GA and the rough endoplasmic reticulum (RER). While the perikarya of all cells contained elements of the GA, only a single process of a subset of type I astrocytes, negative to antibodies A2B5 and HNK-1, contained GA. In contrast, elements of the RER were found within perikarya and all processes. In order to confirm that the immunostained structures in processes indeed represent the GA, we exposed cultures to Brefeldin A (BFA), a secretion blocker which disperses the GA and redistributes it to the RER. We observed that BFA disrupted the GA of both perikarya and processes. However, astrocytes were resistant to prolonged incubations with BFA, while a similar treatment killed cultured fibroblasts and PC-12 cells. Furthermore, in astrocytes exposed to BFA for several days, the delicate network of glial fibrillary acidic protein (GFAP), was replaced by large perinuclear masses of the protein. These observations demonstrate that a subset of type I astrocytes have a single process with elements of the GA. We suggest that this specialization of the GA may be related to yet unrecognized secretory or protein processing functions of these cells. The resistance of astrocytes to BFA and the striking changes in their cytoskeleton induced by the drug, may contribute to studies on the mechanism(s) of action of BFA.

The presence of terminally differentiated slow- and non-dividing cells in the central nervous system (CNS) provides a safe harbor for viral persistence and latency and constitutes a unique immunologic environment for viral infections. Studies of experimental model systems of viral infections of the CNS provide insight into mechanisms of viral persistence and immune-mediated pathology. Nidoviruses are comprised of 2 families of viruses, coronaviruses and arteriviruses, and are common pathogens of humans and a variety of animal species. Both families of viruses contain neurotropic strains that produce experimental neurologic diseases in rodents. These include acute meningitis and encephalitis; acute poliomyelitis; and chronic inflammatory, immune-mediated, demyelination. Coronavirus-induced demyelinating disease mimics many of the pathologic features of Multiple Sclerosis (MS).

Pituitary carcinoma (PC) is a very rare entity (0.2% of all pituitary tumors), with only about 140 cases reported in English literature. There are no reliable histological, immunohistochemical or ultrastructural features distinguishing pituitary adenoma (PA) from PC. By definition, a diagnosis of PC is made after a patient with PA develops non-contiguous central nervous system (CNS) or systemic metastases. To date, only three cases of PC have been reportedly diagnosed on fine needle aspiration (FNA). Two of the reported cases were diagnosed on FNA of the cervical lymph nodes and one on FNA of the vertebral bone lesion. Herein, we present a case of PC, diagnosed on FNA of the liver lesion. In this case, we describe cytologic features of PC and compare them to histologic features of the tumor in the pituitary. Clinical behavior of tumor, pathogenesis of metastasis and immunochemical and prognostic markers will also be described.

The glioneuronal tumor with neuropil-like islands (GTNI) is an uncommon histopathological entity composed of diffuse astrocytic or oligoastrocytic elements interspersed with sharply delimited, micronodular loci of neuronal differentiation. Despite its initial description over 10 years ago [10], the lineage classification of GTNI remains speculative. The clinical features of GTNI, its infiltrative growth characteristics, typically dominating astroglial components, and frequent p53 expression, are all consistent with a fundamental linkage to the diffuse astrocytic tumor group. Supporting this notion are reports documenting, by comparative genomic hybridization, an astrocytoma-like profile of 7q21.1-qter gain and 9p21-pter loss in one case [8] and the absence of oligodendroglioma-associated 1p/19q deletions in a series assessed by polymerase chain reaction-based loss of heterozygosity analysis [3]. Point mutations in the isocitrate dehydrogenase enzymes, IDH1 and IDH2, are found in the majority of WHO grade II and III diffuse gliomas—both astrocytic and oligodendroglial—as well as secondary glioblastomas (GBM), but they are almost entirely absent from primary GBM [7, 9, 11]. As such, they appear to represent a defining early genomic lesion in the pathogenesis of diffuse glioma variants exhibiting step-wise malignant evolution. Glioma-associated IDH mutations invariably involve active site arginine residues—R132 and R172 for IDH1 and IDH2, respectively—and, while their precise pathogenic mechanism remains unclear, they appear to promote the generation of the cancer-predisposing toxic metabolite, R(-)-2-hydroxyglutarate [6]. We assembled 12 cases of GTNI (Table 1) seen at the Memorial Hospital Department of Pathology, along with pertinent clinical information from the patients’ medical records. To evaluate whether IDH1 and IDH2 mutations were present in our sample set, we performed custom genotyping assays on the Sequenom platform [1, 2] and/or employed validated immunohistochemical staining (IHC) for the most common IDH mutation, IDH1 R132H [5]. We found that every tumor in our sample set (12/12) exhibited evidence of the IDH1 R132H mutation by either one or both of our assay methods (Fig. 1a–d), and concordant results were achieved for all cases screened by both Sequenom® and IHC (Table 1). Both glial and neuronal components exhibited immuno-expression of mutant IDH1 in all examined cases (Fig. 1d). Table 1 Cases included in GTNI study cohort listed with patient age at first diagnosis, sex, histopathological grade (Grade), Sequenom® genotyping result (Sequenom) and IHC for IDH1 R132H (R132H IHC) Fig. 1 GTNI is characterized by IDH1 R132H mutations. a A mutation-positive Sequenom® spectrum from a representative GTNI sample displays an additional extension product of different mass, due to the G to A point mutation. Photomicrographs of a representative ... The primary significance of our findings lies in strengthening the pathogenic link between GTNIs and the diffuse glioma tumor group. Studies to date indicate that within primary brain tumors, IDH mutations are largely restricted to diffuse gliomas evolving via step-wise malignant evolution (i.e., diffuse astrocytomas, oligodendrogliomas, and oligoastrocytomas). Combined with the frequent p53 immunoreactivity and general absence of 1p/19q chromosomal co-deletions previously documented in this setting, a high incidence of IDH1 mutations would fundamentally ally GTNIs with the diffuse astrocytoma and 1p/19q-intact oligoastrocytoma group. Indeed, the 100% incidence of IDH mutation in our sample set is even higher than that documented in diffuse astrocytoma so far (~80%) [7, 11]. As an aside, recent work has also identified IDH mutation as a prevalent feature of oligodendrogliomas with neurocytic differentiation [4], further emphasizing that focally prominent neuronal morphology falls well within the histopathological spectrum of diffuse gliomas in general. The invariable presence of the specific IDH1 R132H mutation in our GTNIs may represent an artifact of small sample number, but, nevertheless, it is striking. Whether other IDH1 or IDH2 mutational variants exist in GTNI and whether a genotypic restriction to IDH1 R132H alone would have any functional significance remain unclear.

Two cases of vertebral haemangiomas are reported which presented as spinal cord syndromes during pregnancy. Eleven additional cases of epidural haemangiomas in the literature which became symptomatic during pregnancy are reviewed. In 11 out of 13 cases symptoms presented during the third trimester of pregnancy and in all but two cases the epidural lesions were in the upper six thoracic vertebrae. These features can be explained by the effect of the gravid uterus on the relatively sparse vascular supply of the upper thoracic spinal cord.