Mast cells: new targets for multiple sclerosis therapy?

The majority of brain mast cells in B10.PL mice is present in the hippocampal formation

In the healthy mammalian CNS, mast cells (MCs) are thought to be located mostly in the thalamus. In this study, we have systematically assessed the presence of MCs in the hippocampal formation (HF) and in the thalamus of normal male and female B10.PL mice. Giemsa(+) and Toluidine Blue(+) MCs were detected by histomorphometric analyses at perivascular and intraparenchymal sites of both the hippocampus and the entorhinal cortex. We found a mean number of 4.4 MCs in the HF of female and 3.3 MCs in male B10.PL mice. In contrast to the HF, no MCs were present in the thalamus of these mice. Notably, all HF-MCs showed immunoreactivity for Kit, the receptor for the MC growth and maturation factor SCF, as assessed by FITC-avidin/Kit double labelling. We demonstrate that the majority of brain MCs is found in the hippocampus and entorhinal cortex of B10.PL mice, though the total number of MCs is small compared to other mouse strains or rats. The presence of most brain MCs in the HF of B10.PL mice suggests a potential role of MCs in hippocampal physiology and pathology.

Differential effects of two analgesic drugs, morphine chlorhydrate and acetylsalicylic acid, on thalamic mast cell numbers in rat

Thalamic mast cells (TMCs), the only immunocytes known to infiltrate the brain in physiological conditions, respond to pharmacological agents including sumatriptan - a serotonergic anti-migraine agent - that increases their number. We analysed the effects of two other main analgesics: morphine chlorhydrate, a micro opioid agonist, and acetylsalicylic acid (ASA), a non-steroidal anti-inflammatory drug. All three drugs have specific modes of action, and morphine and ASA, unlike sumatriptan, are also known to interact with peripheral mast cells. Only ASA was effective in promoting TMC number decrease. TMCs, unlike other mast cells, do not express cyclooxygenase (COX) - the key enzyme in the production of prostanoids and the main site of action of ASA - thus dismissing a direct local cellular COX-mediated action. Direct TMC COX-independent mechanisms or effects mediated via distant populations of COX-positive cells such as platelets, leptomeningeal, endothelial and peripheral mast cells are thus probable. ASA, morphine and sumatriptan have distinct TMC effects, suggesting that the TMC number variations they induce are more likely to derive from systemic vasoactive actions than from pharmacological mechanisms devoted to pain relief.

Immunology of multiple sclerosis

Multiple sclerosis (MS) develops in young adults with a complex predisposing genetic trait and probably requires an inciting environmental insult such as a viral infection to trigger the disease. The activation of CD4+ autoreactive T cells and their differentiation into a Th1 phenotype are a crucial events in the initial steps, and these cells are probably also important players in the long-term evolution of the disease. Damage of the target tissue, the central nervous system, is, however, most likely mediated by other components of the immune system, such as antibodies, complement, CD8+ T cells, and factors produced by innate immune cells. Perturbations in immunomodulatory networks that include Th2 cells, regulatory CD4+ T cells, NK cells, and others may in part be responsible for the relapsing-remitting or chronic progressive nature of the disease. However, an important paradigmatic shift in the study of MS has occurred in the past decade. It is now clear that MS is not just a disease of the immune system, but that factors contributed by the central nervous system are equally important and must be considered in the future.

Neuronal TGF-beta1 mediates IL-9/mast cell interaction and exacerbates excitotoxicity in newborn mice

Intraneocortical injection of ibotenate, a glutamate analog, in newborn mice produces damage mimicking lesions observed in human infants with cerebral palsy. Previous research using this model has demonstrated that pretreatment with IL-9, a Th2 cytokine, significantly exacerbated excitotoxic brain lesions. The goal of this study is to identify the underlying pathophysiological mechanism of lesion formation. Pretreatment with TGF-beta1 produced the same effects as IL-9 on ibotenate-induced lesions. IL-9 effects were abolished when a specific TGF-beta1 neutralizing antibody is administered at the same time. Real-time PCR, Western blot, and immunohistochemistry showed that pretreatment with IL-9 increased TGF-beta1 neocortical expression. In vitro studies using real-time PCR and immunocytochemistry demonstrated that neurons were a major contributor in IL-9-induced increase of TGF-beta1. In c-Kit mast cell-deficient mice, TGF-beta1 failed to exacerbate excitotoxic brain lesions, suggesting a key role of mast cells in TGF-beta1 effects. A specific inhibitor of mast cell degranulation and histamine receptor blockers abrogated TGF-beta1 effects on excitotoxic lesions, providing further evidence of mast cell involvement and the role of mast cell-derived histamine. Finally, in vitro studies using a mast cell line showed that TGF-beta1 increased histamine in the supernatant. In aggregate, these data support the notion that neuronal TGF-beta1 plays a key role in the IL-9/mast cell interaction, which leads to an exacerbation of neonatal excitotoxic damage through an increased extracellular histamine concentration. The identification of this pathway, if confirmed in human neonates, might have important implications for understanding and preventing cerebral palsy.

Interferon-beta stabilizes barrier characteristics of brain endothelial cells in vitro

Multiple sclerosis (MS) is accompanied by a breakdown of the blood-brain barrier (BBB) leading to edema formation and aggravation of the disease. Interferon-beta (IFN-beta) has been approved for the treatment of MS and besides its immunomodulatory effects has been demonstrated to lead to a stabilization of BBB integrity in vivo. To investigate whether human recombinant IFN-beta exerts direct effects on the BBB, we used an in vitro BBB model in which brain endothelial cells in coculture with astrocytes form a tight permeability barrier for 3H-inulin and 14C-sucrose. Removal of the astrocytes from the coculture or alternatively addition of histamine resulted in an increased paracellular permeability for small tracers across the brain endothelial cell monolayer. Strikingly, in the presence of IFN-beta, permeability increase under both conditions was inhibited. Permeability changes were accompanied by minor changes in the staining for tight junction-associated proteins in brain endothelial cell monolayers. Taken together, our data demonstrate a direct stabilizing effect of IFN-beta on BBB cerebral endothelial cells in vitro that might significantly contribute to the beneficial effects of IFN-beta treatment in MS in vivo.

Mastocitoma cutâneo canino: estudo de 45 casos

Quarenta e cinco mastocitomas cutâneos caninos foram graduados histologicamente com o uso de hematoxilina-eosina. Foram empregados os métodos azul de toluidina e região organizadora nucleolar argirofílica (AgNOR) para, respectivamente, evidenciar os grânulos citoplasmáticos e avaliar o índice de proliferação celular. Diversas características histológicas foram observadas, como distribuição das células na pele, tamanho, forma, aspecto de citoplasma e núcleo, quantidade de estroma, presença de eosinófilos e alterações associadas. Com base nessas caracteríscas, 37,8% dos mastocitomas foram classificados como grau I, 51,1% como grau II e 11,1% como grau III. A média geral de AgNOR nos mastocitomas foi de 1,9 (1,2 a 4,3) e as médias para os graus I, II e III foram, respectivamente, de 1,5, 1,85 e 3,25. A técnica de AgNOR mostrou ser de fácil execução, custo acessível e confiável como meio auxiliar para estimar um prognóstico mais objetivo para os mastocitomas.

Association between stressful life events and exacerbation in multiple sclerosis: a meta-analysis

OBJECTIVE

To quantify the association between stressful life events and exacerbations of multiple sclerosis.

DATA SOURCES

PubMed, PsychInfo, and Psychological Abstracts searched for empirical papers from 1965 to February 2003 with terms "stress", "trauma", and "multiple sclerosis".

REVIEW METHODS

Three investigators independently reviewed papers for inclusion/exclusion criteria and extracted the relevant data, including methods, sample statistics, and outcomes.

RESULTS

Of 20 studies identified, 14 were included. The meta-analysis showed a significant increase in risk of exacerbation in multiple sclerosis after stressful life events, with a weighted average effect size of d = 0.53 (95% confidence interval 0.40 to 0.65), P < 0.0001. The studies were homogenous, Q = 16.62, P = 0.22, I2 = 21.8%. Neither sampling nor study methods had any effect on study outcomes.

CONCLUSIONS

There is a consistent association between stressful life events and subsequent exacerbation in multiple sclerosis. However these data do not allow the linking of specific stressors to exacerbations nor should they be used to infer that patients are responsible for their exacerbations. Investigation of the psychological, neuroendocrine, and immune mediators of stressful life events on exacerbation may lead to new behavioural and pharmacological strategies targeting potential links between stress and exacerbation.

Ultrastructural evidence of brain mast cell activation without degranulation in monkey experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is an animal model for the human demyelinating disease multiple sclerosis (MS). Increased permeability of the blood-brain barrier (BBB) precedes the development of clinical or pathologic findings in MS and may be induced by perivascular brain mast cells secreting vasoactive and proinflammatory molecules. Brain mast cells were investigated ultrastructurally in acute EAE of the non-human primate common marmoset Callithrix jacchus, which develops a mild neurologic relapsing-remitting course. Control diencephalic samples contained perivascular mast cells with mostly intact electron dense granules. In contrast, EAE samples had marked demyelination and mast cells with numerous altered secretory granules; their electron dense content varied in amount and texture with a "honeycomb" or "target" appearance, but without degranulation. These changes were evident even before the development of any clinical symptoms and suggest that brain mast cells may be involved in EAE, and possibly MS, through a unique process that may involve selective secretion of molecules able to disrupt the BBB.

Immunoglobulin free light chains and mast cells: pivotal role in T-cell-mediated immune reactions?

Immunoglobulin (Ig) free light (L)-chains have long been considered as the meaningless remnants of a spillover in the regular Ig production by B cells. The recently discovered role for Ig free L-chains in mediating hypersensitivity-like responses sheds new light on their potential role in immune responses. Ig free L-chains can sensitize mast cells, such that a second encounter with the appropriate antigen results in mast-cell activation. The possible importance of this reaction for the induction of T-cell-mediated immune reactions, leading to contact sensitivity, multiple sclerosis and rheumatoid arthritis is discussed.