Pathology of choroid plexus in spontaneous immune complex disease and chronic viral infections

The superficial basal lamina of ciliary processes: binding studies with IgG-immunogold and ferritins

In this study, we employed two ultrastructurally visible probing systems, IgG-immunogold and ferritin molecules which differ by surface charge, to study binding activity of the aqueous face of the posterior ciliary processes in short term tissue baths. With these probes we demonstrated that the superficial basal lamina of the non-pigmented epithelium binds monomeric and heat aggregated IgG but not IgG F(ab')2. Binding was inhibited by preincubation with monosaccharides and NaCl suggesting that IgG binding was determined by lectin-like and electrostatic interactions. Anionic binding domains within the basal lamina, capable of exerting an electrostatic influence, were directly demonstrated by selective binding of cationic ferritin species. At high concentrations of cationic ferritin, anionic binding sites were saturated and tracer penetrated the basal lamina to reach intercellular spaces between non-pigmented epithelial cells. We concluded that the superficial basal lamina of the ciliary processes, which is bathed by the aqueous humor, may bind and immobilize IgG, IgG-opsonized antigens and accessible carbohydrate or cations on other molecules in this fluid. This binding may be important in the maintenance of normal aqueous humor composition and in the pathogenesis of infectious and immune-mediated ocular disease.

The expression of major histocompatibility complex (MHC) class I antigens in the brain differs markedly in acute and persistent infections with lymphocytic choriomeningitis virus (LCMV)

Intracranial inoculation of immunocompetent mice with lymphocytic choriomeningitis virus (LCMV) induces a fatal neurologic illness. In this disease a marked increase in MHC class I expression was found, closely associated with viral antigens and inflammatory infiltrates, in meninges, choroid plexus and ventricular ependyma but not within the brain parenchyma. Immunosuppression prevented MHC induction. Mice inoculated at birth had persistent infections, with LCMV antigens found primarily in neurons, but no inflammatory cells or focal increase in MHC class I. Failure of infected neurons to express MHC class I allows them to escape destruction by cytotoxic T cells (CTL) but may increase their susceptibility to be persistently infected by non-lytic viruses.

Class II major histocompatibility complex (MHC) gene expression in the mouse brain is elevated in the autoimmune MRL/Mp-lpr/lpr strain

Brain levels of Ia mRNA, quantified by RNA blot analysis, were found to be 30-50-fold lower than splenic levels in all autoimmune and normal mouse strains examined except MRL/l, whose brain content of Ia mRNA was comparable to normal splenic levels. Prior perfusion to remove blood cells did not alter the amount of Ia mRNA obtainable from MRL/l brain. Elevation of Ia mRNA in MRL/l as compared to control C3H mice was also found in kidney, liver, and spleen, though not in thymus or lung. Results are discussed in relation to an animal model for central nervous system involvement in systemic lupus erythematosus.

Circumventricular organs in chronic serum sickness: a model for cerebral lupus

The pathogenesis of the CNS manifestations of systemic lupus erythematosus (SLE) has been the subject of considerable investigation. The focus of many of these studies has concerned immune complex deposition within the choroid plexus (CP). Involvement of the other brain fenestrated vascular beds, the small, paraventricular circumventricular organs, has not been ascertained. For this purpose, chronic serum sickness, a good immunopathological experimental model of naturally occurring systemic immunological disorders such as SLE, was induced in Wistar rats by prolonged immunization with bovine serum albumin (BSA). The involvement of circumventricular vascular beds by immune deposits was ascertained immunohistochemically. The choroid plexus was found to be the most intensely involved circumventricular structure. Immune complex deposits were also present, in descending order of frequency, in the area postrema, subfornical organ, and pineal gland.

Immunological function of the blood-cerebrospinal fluid barrier

Because the brain lacks a true lymphatic system, it is unclear how peripheral lymphocytes recognize foreign antigens present in the central nervous system. This report demonstrates that the choroid plexus, which constitutes the blood-cerebrospinal fluid barrier, is able to present foreign antigen to, and stimulate the proliferation of, peripheral helper T lymphocytes through an Ia-dependent, major histocompatibility complex-restricted mechanism. Furthermore, in vivo, choroid plexus epithelial cells have access to, and are capable of taking up, virus-sized particles injected elsewhere into the cerebrospinal fluid. Thus these data suggest that the blood-cerebrospinal fluid barrier may play a role in immunological communication between the central nervous system and periphery, a function relevant to the initiation of immunological responses to central nervous system infections and autoimmune processes and for the surveillance of tumor cells in the cerebrospinal fluid.

Immunopathological reactions in viral infections of the central nervous system

Viral infections of the central nervous system (CNS), as of any other organ, evoke humoral and cellular immune responses which enable the host to eliminate the pathogen. However, effective responses may themselves produce tissue damage sometimes exceeding that caused by the virus itself. The relative contribution of the various immunopathological mechanisms in human viral encephalitides remains mostly ill defined. Most of our understanding of the immunopathogenesis in viral CNS infections comes from studies on experimentally infected animals. The prototype model of a virus-induced, cell-mediated, immunopathological CNS disease is the neurological illness of mice that follows intracerebral inoculation with lymphocytic choriomeningitis virus. Virus-specific cytotoxic T cells are crucial to the pathogenesis but death of the animals only results when these cells are targeted into functionally essential brain structures like the circumventricular organs or the medulla oblongata and cervical spinal cord.

Neuropathological features of a lupus-like disorder in autoimmune mice

Neurological syndromes are prominent in systemic lupus erythematosus, but the neuropathological and mechanisms resulting in neurological dysfunction are unknown. We report a neuropathological study of the central nervous system in female NZB/W F1 mice, an animal model of systemic lupus erythematous. NZB/W mice were studied at 3, 5, 8, 12, and 14 months of age, and 36-month-old female C57B16N/NIA mice were studied as aged controls. A lymphoproliferative process was identified in the central nervous system of 39% of 8- to 12-month-old and all 14-month-old NZB/W mice. Infiltrates of lymphocytes and plasma cells were seen in subarachnoid, choroid plexus interstitial, and Virchow-Robin spaces. Lymphoid cells occasionally infiltrated brain parenchyma or accumulated as nodular masses. Concomitant visceral lymphoid infiltration was noted in 14-month-old mice. Dense deposits were seen ultrastructurally in the basal lamina of brain parenchymal capillaries of 14-month-old NZB/W mice. These dense deposits were similar in appearance to immune complexes described in glomerular basal lamina, and appeared concomitantly with an advanced lupus-like glomerulopathy. Similar deposits were not observed in choroid plexus. The possible relevance of these neuropathological changes to human central nervous system lupus is discussed.

Study of protein characteristics that influence entry into the cerebrospinal fluid of normal mice and mice with encephalitis

Entry of proteins into the cerebrospinal (CSF) from the blood is partially determined by the size of the protein. To determine whether other characteristics of proteins influence CSF entry, proteins or protein fragments were iodinated, inoculated intravenously, and serum and CSF were sampled at later times. The Fc fragment of immunoglobulin G (IgG) did not enter the CSF significantly better than the Fab fragment suggesting that choroidal Fc receptors are not of importance for selective immunoglobulin entry. To determine the role of protein charge on entry, bovine serum albumin [isoelectric point (pI) = 3.9] was chemically altered to provide an albumin with an average pI of 6 (A-6) and another with a pI of 8.5 (A-8). All albumins were of the same size on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A-8 entered the CSF approximately 10-fold better than the native albumin. A-6 was intermediate, entering approximately twofold better. At the time of increased CSF protein concentration during an acute viral encephalitis these differences were narrowed but not eliminated. It is concluded that charge is an important determinant of protein entry into the CSF.

The neuropathology of rheumatoid disease

Patients with active rheumatoid disease may develop encephalopathy, myelopathy, peripheral neuropathy, and myopathy through a variety of tissue mechanisms. Brain involvement is usually characterized by the formation of rheumatoid nodules or by the development of vasculitis or its complications, and there is evidence to suggest that the trapping of immune complexes within the choroid plexus may be important in pathogenesis. Structural damage to the spinal cord and lower brain stem, on the other hand, most commonly results from narrowing of the bony canal, leading either to direct compression of neural tissue or to compromise of its vascular supply. The appearance of peripheral neuropathy generally signifies the presence either of inflammatory epineurial arterial disease or entrapment by neighboring anatomical structures. Skeletal muscle dysfunction may be due to vasculitis, myositis, or denervation atrophy. Both systemic and local anatomical factors, therefore, are of importance in determining the manner in which different parts of the nervous system may be affected in rheumatoid disease.

Rat CNS in experimental chronic serum sickness: integrity of the zonulae occludentes of the choroid plexus epithelium and brain endothelium in experimental chronic serum sickness

The present study is an extensive systematic immunofluorescence and labelled electron microscopic investigation of chronic rat serum sickness brains. It is specifically directed at discerning effects of chronic serum sickness upon the zonulae occludentes of both the choroid plexus epithelium and the intra-cerebral endothelium. Although the choroid plexus is a known site of complex entrapment in systemic immune complex disorders, comprehensive immune studies of the CNS parenchymal vasculature have not yet been reported in either experimental or spontaneous immune complex disease. We examined by direct immunofluorescence techniques over 70 blocks of experimental chronic serum sickness brains taken from 16 animals with severe glomerular disease and found them to be uniformly negative for the presence of immune deposits. No horseradish peroxidase was seen beyond the restricting zonulae occludentes of either the choroid plexus or the cerebral endothelium in tissue from three serious affected animals. These structural barriers retained their integrity despite the extensive circulation and deposition of complexes and complement induced in the experimental model and the associated release of vasoactive substances.

[Demonstration of total complement in normal cerebrospinal fluid]

Até o presente momento, todos os autores afirmam que o líquido cefalorraqueano (LCR) normal do homem não apresenta atividade hemolítica do complemento total. Alguns pesquisadores verificaram, entretanto, a presença de todos os quatro componentes em muitas amostras de LCR normal sem conseguir, porém, demonstrar a atividade hemolítica do complemento total. Este fato parecia indicar que o LCR normal era desprovido da atividade hemolítica do complemento total provavelmente por motivo da concentração insuficiente de suas proteínas. Para investigar esta hipótese foi feita uma prova preliminar, concentrando 10 amostras de LCR normal, dividindo-se o concentrado em duas partes, uma das quais foi inativada à temperatura de 56°C, durante 20 minutos. Esta prova revelou hemólise das hemácias sensibilizadas somente em relação com o LCR concentrado ativo. Em prosseguimento foram feitas pesquisas em 108 amostras de LCR normal obtidas por punção cisternal, selecionadas de pacientes sem doença de ordem geral, porém com perturbações neurológicas ou psíquicas que, em geral, não costumam determinar alterações do LCR. As amostras de LCR foram concentradas vinte vezes o seu volume, pelo método da diálise sob pressão negativa em camisa de colódio, segundo o processo de Mies. Esta pesquisa proporcionou resultados que permitiram concluir que o líquido cefalorraqueano normal concentrado apresenta atividade hemolítica do complemento total em 98% dos casos. O título do complemento total variou de 0 a 23 unidades de hemólise 50% em 1 ml de líquido concentrado.

Ferritin immune complex deposits in the choroid plexus

Mice injected intraperitoneally with 20 mg of ferritin twice weekly for more than 4 weeks developed proteinuria due to the deposition of ferritin-antiferritin antibody complexes in renal glomeruli. Deposits of ferritin, immunoglobulin G (IgG) and third complement component (C3) also accumulated in the perivascular, extracellular space of the choroid plexus as demonstrated by immunofluorescence and electron microscopy. The findings confirm previous observations on immune complex deposits in the choroid plexus in spontaneous autoimmune disease and persistent viral infections. The occurrence of similar deposits in the human choroid plexus and the possibility of an associated disturbance of the blood-spinal fluid barrier are discussed.

Mesangiocapillary glomerulonephritis in lambs. III. Quantitative and qualitative aspects of immunopathology

Newborn Finnish Landrace lambs subsequently affected with mesangiocapillary glomerulonephritis (MCGN) were deficient in the third component of complement (C'3), serum levels being approximately 5 per cent. of those in unaffected lambs. Hypocomplementaemia persisted until symptoms of renal failure occurred at around 6-8 wk of age. Immunofluorescence examinations of renal cortex with antisera specific for IgG, IgM, IgA, C'3 and fibrin supported previous morphological evidence of a strong similarity between this disease and MCGN in man. Similar examinations of choroid plexus suggested that immune complexes containing IgG, IgM and C'3 were present in the interstitium.