Absence of IFN-γ or IL-12 Has Different Effects on Experimental Myasthenia Gravis in C57BL/6 Mice

Abstract

Immunization with acetylcholine receptor (AChR) causes experimental myasthenia gravis (EMG). Th1 cells facilitate EMG development. IFN-γ and IL-12 induce Th1 responses: we investigated whether these cytokines are necessary for EMG development. We immunized wild-type (WT) C57BL/6 mice and IFN-γ and IL-12 knockout mutants (IFN-γ−/−, IL-12−/−) with Torpedo AChR (TAChR). WT and IFN-γ−/− mice developed EMG with similar frequency, IL-12−/−mice were resistant to EMG. All strains synthesized anti-AChR Ab that were not IgM or IgE. WT mice had anti-AChR IgG1, IgG2b, and IgG2c, IFN-γ−/− mice had significantly less IgG2c, and IL-12−/− mice less IgG2b and IgG2c. All mice had IgG bound to muscle synapses, but only WT and IFN-γ−/− mice had complement; WT mice had both IgG2b and IgG2c, IFN-γ−/− only IgG2b, and IL-12−/− neither IgG2b nor IgG2c. CD4+ cells from all AChR-immunized mice proliferated in response to AChR and recognized similar epitopes. After stimulation with TAChR, CD4+ cells from IFN-γ−/− mice secreted less IL-2 and similar amounts of IL-4 and IL-10 as WT mice. CD4+ cells from IL-12−/− mice secreted less IFN-γ, but more IL-4 and IL-10 than WT mice, suggesting that they developed a stronger Th2 response to TAChR. The EMG resistance of IL-12−/− mice is likely due to both reduction of anti-TAChR Ab that bind complement and sensitization of modulatory Th2 cells. The reduced Th1 function of IFN-γ−/− mice does not suffice to reduce all complement-fixing IgG subclasses, perhaps because as in WT mice a protective Th2 response is missing.

Effect of complement and its regulation on myasthenia gravis pathogenesis

“…Animal models, which induce EAMG either by administration of AChR antibodies or immunization with purified AChR, support the hypothesis: complement drives pathology in mouse and rat EAMG [49,50]; agents that block, inhibit or deplete complement protect animals from EAMG [51][52][53]; mice with a genetic deficit in complement components are resistant or less susceptible to EAMG [54]; inability to activate complement is associated with many immunological factors (e.g., in IL-12-deficient mice) [55], antibody, C3, C9 and MAC are uniformly found at the junctions of EAMG animals; and mice deficient in cell surface regulators of complement are particularly susceptible to EAMG induced by administration of AChR antibodies [50,56,57]. The following sections discuss the function of individual complement components as they relate primarily to EAMG pathogenesis.…”

CCL2 recruitment of IL‐6‐producing CD11b+ monocytes to the draining lymph nodes during the initiation of Th17‐dependent B cell‐mediated autoimmunity

“…Although earlier work had indicated that ectopic expression of IFN-c at the neuromuscular junction provoked MG-like disease [33], our current understanding of the role of IFN-c in EAMG is far from conclusive. For example, mice deficient of IFN-c [25] or IFN-c receptor [26] are resistant to EAMG, yet some groups have shown that IFN-c deficiency may not significantly alter the course of disease [27,34]. Thus, while Th1 responses may possibly play a role in the disease depending on the experimental system used, the question arises on whether other inflammatory cytokine(s) with potent propathogenic effects, such as IL-17, are required for the expression of EAMG.…”

“…We and others [25][26][27] have previously found that the development of EAMG is not dramatically altered by IFN-c deficiency. To investigate whether the effects of IL-17 on EAMG were related to or depended on IFN-c, we treated IFN-c -/-mice with IL-17 during EAMG induction, using the same regimen used for the B6 mice.…”

“…edrophonium chloride (Reversol; Organon, West Orange, NJ), a cholinesterase inhibitor that immediately increases the strength of mice that have clinical EAMG. To further verify the extent of EAMG, we quantified the muscle AChR content by radioimmunoassay using 125 I-labeled a-bungarotoxin, (Amersham Corp., Arlington Heights, IL) [27].…”

Dendritic cells exposed in vitro to TGF-beta1 ameliorate experimental autoimmune myasthenia gravis

“…wild-type mice [31]. IFN-g neutralization strongly influenced the Th1/Th2 balance but did not affect the disease outcome, indicating that a Th1-dominated immune response is not necessarily associated with disease severity in EAMG [32].…”