Immune control of the brain

Extracellular membrane vesicles and immune regulation in the brain

The brain is characterized by a complex and integrated network of interacting cells in which cell-to-cell communication is critical for proper development and function. Initially considered as an immune privileged site, the brain is now regarded as an immune specialized system. Accumulating evidence reveals the presence of immune components in the brain, as well as extensive bidirectional communication that takes place between the nervous and the immune system both under homeostatic and pathological conditions. In recent years the secretion of extracellular membrane vesicles (EMVs) has been described as a new and evolutionary well-conserved mechanism of cell-to-cell communication, with EMVs influencing the microenvironment through the traffic of bioactive molecules that include proteins and nucleic acids, such as DNA, protein coding, and non-coding RNAs. Increasing evidence suggests that EMVs are a promising candidate to study cross-boundary cell-to-cell communication pathways. Herein we review the role of EMVs secreted by neural cells in modulating the immune response(s) within the brain under physiological and pathological circumstances.

Marcação imunoistoquímica da expressão astrocitária de proteína glial fibrilar ácida e de vimentina no sistema nervoso central de cães com cinomose

Uma vez que muitos dos aspectos envolvidos na patogenia dos processos desmielinizantes do sistema nervoso central (SNC) são ainda pouco esclarecidos e que os astrócitos parecem estar envolvidos na mediação de tais processos, este estudo analisou morfologicamente a participação astrocitária na desmielinização do SNC por meio da marcação imunoistoquímica de duas proteínas dos filamentos intermediários astrocitários - a proteína glial fibrilar ácida (GFAP) e a vimentina (VIM) -, comparando amostras de cerebelo e de tronco encefálico de oito cães com cinomose e de dois cães normais, de diferentes raças e com idades entre um e quatro anos. Cortes histológicos dos tecidos foram submetidos à marcação pelo método indireto da avidina-biotina-peroxidase (ABC) e a reatividade astrocitária, observada em microscopia de luz, foi quantificada em um sistema computacional de análise de imagens. Observou-se, na maioria dos cortes de animais doentes, a presença de lesões degenerativas compatíveis com desmielinização. A marcação para a GFAP e para a VIM foi mais intensa nos animais com cinomose do que nos animais normais, especialmente nas regiões circunventriculares e nas adjacentes às áreas de degeneração tecidual. Não houve diferença significativa entre a imunomarcação (GFAP e VIM) dos animais com cinomose com e sem infiltração inflamatória da substância branca do cerebelo. O aumento da imunorreatividade dos astrócitos para a GFAP e a reexpressão de VIM nas áreas lesionais indicam o envolvimento astrocitário na resposta do tecido nervoso às lesões desmielinizantes induzidas pelo vírus da cinomose (CDV) no SNC.

Development of an Animal Model for Neurocysticercosis: Immune Response in the Central Nervous System Is Characterized by a Predominance of γδ T Cells

Neurocysticercosis is the most common parasitic disease of the central nervous system worldwide. It is caused by the metacestode form of the helminth Taenia solium. Study of the immune response in the human brain has been limited by the chronic progression of the disease, the influence of corticosteroid treatment, and the scarcity of patients who undergo surgical intervention. To better understand the immune response and associated pathology in neurocysticercosis, a mouse model was developed by intracranial infection of BALB/c mice with Mesocestoides corti, a cestode organism related to T. solium. The immune response reveals the presence of abundant inflammatory infiltrates appearing as early as 2 days postinfection in extraparenchymal regions. In contrast, infiltration of immune cells into parenchymal tissue is significantly delayed. There is a natural progression of innate (neutrophils and macrophages), early induced (NK cells and γδ T cells), and adaptive immune responses (αβ T cells and B cells) in infected mice. γδ T cells are the predominant T cell population. A cell-mediated Th1 pathway of cytokine expression is evident in contrast to the previously described Th2 phenotype induced in the periphery.

Pathogenetic role of phagocytic abnormalities in human virus immunodeficiency infection: possible therapeutical approaches. A review

Polymorphonuclear cells (PMN) and monocytes/macrophages (M/M) represent the first defence line against invading microorganisms. Both phagocytic cell functions are precociously compromised in human immunodeficiency virus (HIV)-infected subjects, thus leading to infectious and neurological complications in the late stages of disease. Among intracellular pathogens, emerging bacteria such as Bartonella henselae and Rhodococcus equi can cause peculiar clinical pictures, i.e. the bacillary parenchimal angiomatosis and a classical pyogranulomatous broncopneumonia, respectively. On the other hand, overproduction of proinflammatory cytokines (CKs) and, in particular, tumor necrosis factor-alpha under HIV or lipopolysaccharide stimulation may cause neural damage in terms of demyelination and subsequent development of acquired immunodeficiency syndrome (AIDS) dementia complex. Some therapeutical attempts have been made with colony stimulating factors in order to increase the number and potentiate the function of PMN and M/M. On the other hand, the use of drugs able to reduce exaggerated release of CKs by M/M is suggested in AIDS patients in order to prevent a further aggravation of the clinical condition.