Acute experimental autoimmune encephalomyelitis. Differences between T cell subsets in the blood and meningeal infiltrates in susceptible and resistant strains of guinea pigs

Immune-mediated CNS damage

Multiple sclerosis (MS) is a demyelinating autoimmune disease. However, the persisting neurological deficits in MS patients result from acute axonal injury and chronic neurodegeneration, which are both triggered by the autoreactive immune response. Innate immunity, mainly mediated by activated microglial cells and invading macrophages, appears to contribute to chronic neurodegeneration. Activated microglia produce several reactive oxygen species and proinflammatory cytokines which affect neuronal function, integrity and survival. Adaptive immunity, particularly in cytotoxic CD8+ T cells, participates in acute demyelination and axonal injury by directly attacking oligodendrocytes and possibly neurons as well. Understanding the mechanisms of immune-mediated neuronal damage might help to design novel therapy strategies for MS.

Mature bone marrow-derived dendritic cells polarize Th2 response and suppress experimental autoimmune encephalomyelitis

Distinct subsets of dendritic cells (DCs) based on the origin, phenotypes, and the nature of the signals that promote DC maturation can determine polarized immune responses of T cells. In this study, DCs were cultured from mouse bone marrow (BM) progenitors in granulocyte-macrophage colony-stimulating factor (GM-CSF). To generate mature DCs (mDCs), lipopolysaccharide (LPS) was used in the culture for 24 h. LPS-stimulated DCs were phenotypically mature, which exhibited strongly upregulated CD40, B7.1, and B7.2 compared to non-LPS-stimulated immature DCs (imDCs). Both mDCs and imDCs expressed high levels of MHC class II but low level of CD54. mDCs produced higher levels of IL-10 and lower IL-12 compared to imDCs. No IFN-gamma or IL-4 was found in both groups. When mDCs were injected intraperitoneally (i.p.) to the mice with experimental autoimmune encephalomyelitis (EAE), the severity of clinical signs and inflammation in the CNS was significantly suppressed compared to imDC-injected mice (p<0.01) and PBS-injected mice (p<0.02). Moreover, lymphocytes from mDC-injected mice produced lower level of IL-12, IFN-gamma, but higher level of IL-10, compared to imDC-injected and non-DC-injected mice. We conclude that BM-mDCs, but not BM-imDCs, promote Th2 differentiation and have the potential for suppression of inflammatory demyelination.

Magnetic resonance imaging investigation of blood-brain barrier damage in adoptive transfer experimental autoimmune encephalomyelitis

Recent advances in fast magnetic resonance imaging (MRI) techniques have allowed quantification of parameters such as T1 relaxation time, which can be modified by changes in the water content of a tissue. We have used this new method to study the evolution of blood-brain barrier (BBB) changes after adoptive transfer of MBP-specific (AT-EAE) and ovalbumin-specific T cell lines in Lewis rats. Measurable changes in T1 relaxation time suggesting widespread increase in BBB permeability were found, starting on day 3 post inoculation (p.i.), in the midbrain and brainstem of AT-EAE rats. In addition, we noted a significant decrease in T1 relaxation time before injection of a paramagnetic agent, in the cisternal cerebrospinal fluid (CSF) of diseased animals, starting on day 5 p.i. In vitro measurement of T1 in CSF containing various concentrations of albumin, IgM and glucose showed that, at physiological concentrations, a T1 decrease is mainly associated with an increase in albumin concentration. A moderate increase in BBB and blood-CSF barrier permeability was found as early as 4-8 h p.i., in rats injected with MBP-specific as in animals injected with ovalbumin-specific T cell lines, suggesting a non-specific mechanism. Experimental MRI may become a powerful tool to sequentially analyse changes in barrier dynamics, for example following pharmacological intervention.

Experimental allergic encephalomyelitis in guinea pig: variability of response to intradermal emulsion injection

Different forms of experimental allergic encephalomyelitis were obtained in 4 groups of guinea pigs: 7 adult Hartley guinea pigs (Group I), 12 adults of the same strain (Group II), 6 juvenile strain 2 guinea pigs (Group III) and 6 juvenile strain 13 animals (Group IV), by the injection of emulsions. Groups I and II received emulsions containing 250 mg and 500 mg respectively of fresh isologous spinal cord tissue, complete Freund adjuvant (CFA) and saline solution while Groups III and IV received an emulsion containing 120 mg of isologous spinal cord, CFA, saline solution and 15 mg of Mycobacterium tuberculosis. The increased antigen load induced a disease with delayed onset and prolonged progressive course (C-P-EAE) in Groups I and II, although 8 animals showed no symptoms of illness. The findings in C-P-EAE were large demyelinated plaques, perivenous fibrosis and large areas of infiltration. Demyelinated areas occurred within the spinal cord white matter only in two asymptomatic animals. C-P-EAE was obtained in 4 of the Strain 2 animals. In conclusion, the increased antigen load induced a range of lesions in Hartley guinea pigs, although not all animals were affected. C-P-EAE was induced also in strains of guinea pig other than the Heartley strain. These different reactions may have been the outcome of partial or complete inactivation of the cell-mediated response to the inoculated antigens.

Identification and quantitation of the expression of T cell surface markers during the development of chronic relapsing experimental allergic encephalomyelitis (CREAE) in the guinea pig

As there were discrepancies in previous data on the T cell nature of cells infiltrating the meninges at all stages of chronic relapsing experimental allergic encephalomyelitis (CREAE), experiments have been performed using a further monoclonal antibody (Mab) recognizing total T cell populations and the classic E rosetting technique. Cytospins were prepared of the meningeal inflammatory cells obtained by washing the brains of these animals, and stained by indirect immunoperoxidase. It was found that the T cell, as defined by both E rosetting and staining with the Mab CT5, is the major cell type found in the meninges during the development of CREAE. However, the staining with the Mab CT7, which recognizes a functionally relevant antigen, showed that there is a discrepancy between the numbers of lymphocytes stained compared to the results with CT5 and E rosettes. Furthermore, the antigen recognized by CT7 appeared to be modulated during the disease. The possible functional relevance and its relation to clinical remission and relapse are discussed.

Adoptive transfer of murine chronic-relapsing autoimmune encephalomyelitis. Analysis of basic protein-reactive cells in lymphoid organs and nervous system of donor and recipient animals

Frequency analysis of myelin basic protein (MBP)-reactive lymphocytes was performed in the chronic relapsing murine experimental allergic encephalomyelitis (EAE) model induced by the adoptive transfer of myelin basic protein (MBP)-primed lymphocytes to naive recipients. During the first attack, MBP-reactive cell frequencies were: 1/41,700 in spleen, 1/328,000 in lymph nodes, 1/64,500 in the peripheral blood. After recovery from a second attack, the frequencies were: 1/11,000 in spleen, 1/46,000 in lymph node, and 1/195,000 in the blood. In addition, lymph node cells obtained from animals following a second attack had increased encephalitogenic properties. CNS-derived lymphocytes analyzed during the first attack were 50% Lyt 1.2+ and 16% Lyt 2.2+. After recovery from the second attack, phenotypes were 20% Lyt 1.2+ and 49% Lyt 2.2+. There were only minimal responses to MBP in CNS-derived lymphocytes. Susceptibility to adoptively transferred EAE was in general predicted by whether a proliferative response to MBP occurred following immunization and was not solely H-2 linked. These studies demonstrate an accumulation of autoreactive cells in the spleen and lymph nodes and a shift of the phenotype of cells in the target organ as EAE becomes chronic and suggest there are dynamic immunologic processes, both in the peripheral immune system and target organ associated with relapsing EAE.