The Th2 cytokine IL-4 is not required for the progression of antibody- dependent autoimmune myasthenia gravis

Experimental autoimmune myasthenia gravis (EAMG), a disorder of the neuromuscular junction, is mediated by autoantibodies against muscle nicotinic acetylcholine receptor (AChR). The roles of IFN-γ (Th1) and IL-4 (Th2) cytokines in the initiation and progression of this disease are not fully understood. Recently, we have demonstrated that IFN-γ is necessary for the initiation of tAChR-induced EAMG in mice. However, the role of IL-4 in the progression of clinical EAMG remained undetermined. In this study we have addressed the contribution of IL-4 in the disease progression in IL-4(-/-) C57BL/6j mice whose IL-4 gene has been disrupted. Following immunization with Torpedo (t) AChR, the IL-4(-/-) mice readily developed signs of muscle weakness and succumbed to clinical EAMG with kinetics similar to the susceptibility of IL-4(+/+) mice. The tAChR-primed lymph node cells from IL- 4(-/-) mice vigorously proliferated to tAChR and to its dominant α_{146- 162} sequence associated with disease pathogenesis. However, these T cells secreted higher levels of IFN-γ and IL-2, suggesting the development of a Th1 default pathway in these mice. Nevertheless, the IL-4 mutation had no effect on the recruitment of CD4⁺Vβ6⁺ T cells specific to the dominant tAChR α_146-162 sequence in vivo. Immune sera from IL-4(-/-) mice showed a dramatic increase in mouse AChR-specific IgG2a levels followed by a concomitant decrease in IgG1 levels, but these mice did not exhibit an accelerated disease. In conclusion, we have demonstrated for the first time that IL-4 is not required either for the generation of a pathogenic anti- AChR humoral immune response or for progression of clinical EAMG in mice.