Regulatory T cells induced by GM-CSF suppress ongoing experimental myasthenia gravis

A GMCSF-neuroantigen fusion protein is a potent tolerogen in experimental autoimmune encephalomyelitis (EAE) that is associated with efficient targeting of neuroantigen to APC

Cytokine-NAg fusion proteins represent an emerging platform for specific targeting of self-antigen to particular APC subsets as a means to achieve antigen-specific immunological tolerance. This study focused on cytokine-NAg fusion proteins that targeted NAg to myeloid APC. Fusion proteins contained GM-CSF or the soluble extracellular domain of M-CSF as the N-terminal domain and the encephalitogenic 69-87 peptide of MBP as the C-terminal domain. GMCSF-NAg and MCSF-NAg fusion proteins were approximately 1000-fold and 32-fold more potent than NAg in stimulating antigenic proliferation of MBP-specific T cells, respectively. The potentiated antigenic responses required cytokine-NAg covalent linkage and receptor-mediated uptake. That is, the respective cytokines did not potentiate antigenic responses when cytokine and NAg were added as separate molecules, and the potentiated responses were inhibited specifically by the respective free cytokine. Cytokine-dependent targeting of NAg was specific for particular subsets of APC. GMCSF-NAg and MCSF-NAg targeted NAg to DC and macrophages; conversely, IL4-NAg and IL2-NAg fusion proteins, respectively, induced an 1000-fold enhancement in NAg reactivity in the presence of B cell and T cell APC. GMCSF-NAg significantly attenuated severity of EAE when treatment was completed before encephalitogenic challenge or alternatively, when treatment was initiated after onset of EAE. MCSF-NAg also had significant tolerogenic activity, but GMCSF-NAg was substantially more efficacious as a tolerogen. Covalent GMCSF-NAg linkage was required for prevention and treatment of EAE. In conclusion, GMCSF-NAg was highly effective for targeting NAg to myeloid APC and was a potent, antigen-specific tolerogen in EAE.

Acetylcholine receptor-alpha subunit expression in myasthenia gravis: a role for the autoantigen in pathogenesis?

Previous studies have shown increased expression of acetylcholine receptor-alpha (AChR-alpha) subunit transcripts in myasthenia gravis (MG) and experimental MG (EAMG), but none examined the functional properties of this overexpression. In this study we examined the mRNA and protein expression of AChR-alpha as well as the pattern of alpha-bungarotoxin labeling in muscle tissue from EAMG mice with varying disease severity. AChR-alpha expression was increased considerably in endplates from mice with severe EAMG, but it was distinct and greatly in excess of alpha-bungarotoxin labeling. This "aberrant expression" occurred in mice with morphologic endplate damage, and the pattern of complement and immunoglobulin deposition in muscle from these mice appeared to mirror the pattern of AChR-alpha expression. The loss of functional AChR in severe MG increases transcription of AChR-alpha mRNA, but the expressed protein is "functionally inert," failing to compensate for loss of AChR. This enhanced expression of AChR may play a role in driving the ongoing autoimmune response. Muscle Nerve 40: 279-286, 2009.

Autoimmune myasthenia gravis: emerging clinical and biological heterogeneity

Acquired myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction in which patients experience fluctuating skeletal muscle weakness that often affects selected muscle groups preferentially. The target of the autoimmune attack in most cases is the skeletal muscle acetylcholine receptor (AChR), but in others, non-AChR components of the neuromuscular junction, such as the muscle-specific receptor tyrosine kinase, are targeted. The pathophysiological result is muscle endplate dysfunction and consequent fatigable muscle weakness. Clinical presentations vary substantially, both for anti-AChR positive and negative MG, and accurate diagnosis and selection of effective treatment depends on recognition of less typical as well as classic disease phenotypes. Accumulating evidence suggests that clinical MG subgroups might respond differently to treatment. In this Review, we provide current information about the epidemiology, immunopathogenesis, clinical presentations, diagnosis, and treatment of MG, including emerging therapeutic strategies.

GM-CSF and IL-4 synergistically trigger dendritic cells to acquire retinoic acid-producing capacity

Retinoic acid (RA) produced by intestinal dendritic cells (DCs) imprints gut-homing specificity on lymphocytes and enhances Foxp3⁺ regulatory T-cell differentiation. The expression of aldehyde dehydrogenase (ALDH) 1A in these DCs is essential for the RA production. However, it remains unclear how the steady-state ALDH1A expression is induced under specific pathogen-free (SPF) conditions. Here, we found that bone marrow-derived dendritic cells (BM-DCs) generated with granulocyte-macrophage colony-stimulating factor (GM-CSF) expressed Aldh1a2, an isoform of Aldh1a, but that fms-related tyrosine kinase 3 ligand-generated BM-DCs did not. DCs from mesenteric lymph nodes (MLN) and Peyer's patches (PP) of normal SPF mice expressed ALDH1A2, but not the other known RA-producing enzymes. Employing a flow cytometric method, we detected ALDH activities in 10–30% of PP-DCs and MLN-DCs. They were CD11c^highCD4^−/lowCD8α^intermediateCD11b^−/low F4/80^{low/intermediate}CD45RB^lowCD86^highMHC class II^highB220⁻CD103⁺. Equivalent levels of aldehyde dehydrogenase activity (ALDHact) and ALDH1A2 expression were induced synergistically by GM-CSF and IL-4 in splenic DCs in vitro. In BM-DCs, however, additional signals via Toll-like receptors or RA receptors were required for inducing the equivalent levels. The generated ALDH1A2⁺ DCs triggered T cells to express gut-homing receptors or Foxp3. GM-CSF receptor-deficient or vitamin A-deficient mice exhibited marked reductions in the ALDHact in intestinal DCs and the T cell number in the intestinal lamina propria, whereas IL-4 receptor-mediated signals were dispensable. GM-CSF⁺CD11c⁻F4/80⁺ cells existed constitutively in the intestinal tissues. The results suggest that GM-CSF and RA itself are pivotal among multiple microenvironment factors that enable intestinal DCs to produce RA.