Andreas Holz

Myelin-associated oligodendrocytic basic protein: identification of an encephalitogenic epitope and association with multiple sclerosis.

Myelin-associated oligodendrocytic basic protein (MOBP) is an abundant myelin constituent expressed exclusively by oligodendrocytes, the myelin-forming cells of the CNS. We report that MOBP causes experimental allergic encephalomyelitis and is associated with multiple sclerosis. First, we note that purified recombinant MOBP inoculated into SJL/J mice produces CNS disease. Tests of overlapping peptides spanning the murine MOBP molecule map the encephalitogenic site to amino acids 37–60. MOBP-induced experimental allergic encephalomyelitis shows a severe clinical course and is characterized by a prominent CD4+ T lymphocyte infiltration and a lesser presence of CD8+ T cells and microglia/macrophages around vessels and in the white matter of the CNS. Second, PBL obtained from patients with relapsing/remitting multiple sclerosis mount a proliferative response to human MOBP, especially at amino acids 21–39. This response equals or exceeds the response to myelin basic protein and an influenza virus hemagglutinin peptide, both serving as internal controls. Thus, a novel myelin Ag, MOBP aa 37–60, plays a role in rodent autoimmune CNS disease, and its human MOBP counterpart is associated with the human demyelinating disease multiple sclerosis.

Constitutive β cell expression of IL-12 does not perturb self-tolerance but intensifies established autoimmune diabetes

To analyze the function of the Th1-promoting cytokine IL-12 in vivo, we generated transgenic (tg) mice (RIP-IL12 mice) whose pancreatic beta cells constitutively express bioactive IL-12 or one of its components, p35 or p40. In contrast to non-tg littermates or single-tg RIP-p35 and RIP-p40 mice, RIP-IL12 mice developed a marked pancreatic infiltration of lymphocytes and macrophages, mainly around islets. Expression of bioactive IL-12 primarily upregulated transcript levels of IFN-inducible protein-10 (IP-10), RANTES, IFN-gamma, and TNF-alpha in the pancreas. Despite the substantial recruitment of mononuclear cells, no biochemical or clinical disease was evident in the exocrine or endocrine pancreas. Coexpression of lymphocytic choriomeningitis virus (LCMV) proteins with IL-12 in the beta cells failed to spontaneously activate or expand antigen-specific anti-self/viral T cells in uninfected tg animals. However, when RIP-IL12 x RIP-LCMV tg mice were infected with LCMV, antigen-specific anti-self/viral T cells were induced, which led to an acceleration in the kinetics and severity of insulin-dependent diabetes mellitus (IDDM). Thus, the ectopic expression of IL-12 does not spontaneously break tolerance and activate antigen-specific T cells in the periphery, but it does worsen ongoing autoimmune disease.

Neither B lymphocytes nor antibodies directed against self antigens of the islets of Langerhans are required for development of virus-induced autoimmune diabetes.

We evaluated the role of the humoral arm of the immune response in causing or contributing to virus-induced diabetes. Transgenic mice expressing the nucleoprotein (NP) or glycoprotein (GP) of the lymphocytic choriomeningitis virus (LCMV) under control of the rat insulin promoter (RIP) in pancreatic β cells (RIP-LCMV) and RIP-LCMV mice with genetic dysfunction of B cells (RIP-LCMV × μMT/μMT) were compared for development of diabetes after challenge with LCMV. After inoculation with LCMV, B and T lymphocytes and macrophages infiltrated into pancreatic islets in RIP-LCMV mice, and over 50% of these mice generated Abs against host insulin or glutamate decarboxylase. However, neither B cells nor the autoantibodies played a direct role in the initiation, kinetics, or severity of the virus-induced diabetes as judged by comparing disease in RIP-LCMV mice to littermates whose functional B cells were genetically eliminated. Furthermore, the quality and quantity of T lymphocyte and macrophage infiltration was similar in the B cell-deficient and non-B cell-deficient RIP-LCMV mice. Although the development of autoantibodies to islet Ags had no direct influence on the pathogenesis of insulin-dependent (type 1) diabetes mellitus, it served as a prediabetes marker, as such autoantibodies were often elevated before the onset of disease. Hence, the RIP-LCMV model is not only useful for understanding the pathogenetic mechanisms of how islets are destroyed and spared but also for evaluating therapeutic strategies before onset of clinical diabetes.

A new approach for evaluating antigen-specific T cell responses to myelin antigens during the course of multiple sclerosis

We used a flow cytometry assay to measure proliferation and cytokine production of self-antigen-specific T cells in individual patients during the clinical course of multiple sclerosis (MS). Myelin-associated oligodendrocytic basic protein (MOBP) was selected for proof of principles in the assay, along with myelin basic protein (MBP) to assess specific activated T cells in 10 MS patients over an 18-month period, in parallel with brain magnetic resonance imaging (MRI) scans and clinical rating scale. A positive correlation occurred between antigen-specific T cell proliferation and interferon-gamma production with clinical relapses and MRI lesion activity that was absent when the same patients were in remission.