RESUMO
Nucleated cells are equipped with several mechanisms that support their resistance to complement-dependent cytotoxicity (CDC). The role of the NF-κB pathway in cell protection from CDC was examined. Elevated sensitivity to CDC was demonstrated in cells lacking the p65 subunit of NF-κB or the IκB kinases IKKα or IKKß, and in cells treated with p65 small interfering RNA. Pretreatment with the IKK inhibitor PS-1145 also enhanced CDC of wild-type cells (WT) but not of p65(-/-) cells. Furthermore, reconstitution of p65 into p65(-/-) cells and overexpression of p65 in WT cells lowered their sensitivity to CDC. The postulated effect of p65 on the JNK-mediated death-signaling pathway activated by complement was examined. p65 small interfering RNA enhanced CDC in WT cells but not in cells lacking JNK. JNK phosphorylation induced by complement was more pronounced in p65(-/-) cells than in WT cells. The results indicate that the NF-κB pathway mediates cell resistance to CDC, possibly by suppressing JNK-dependent programmed necrotic cell death.
Assuntos
Ativação do Complemento/imunologia , Complexo de Ataque à Membrana do Sistema Complemento/fisiologia , Citotoxicidade Imunológica/imunologia , Transdução de Sinais/imunologia , Fator de Transcrição RelA/fisiologia , Animais , Comunicação Celular/genética , Comunicação Celular/imunologia , Ativação do Complemento/genética , Complexo de Ataque à Membrana do Sistema Complemento/deficiência , Complexo de Ataque à Membrana do Sistema Complemento/metabolismo , Citotoxicidade Imunológica/genética , Células-Tronco Embrionárias/enzimologia , Células-Tronco Embrionárias/imunologia , Células-Tronco Embrionárias/metabolismo , Fibroblastos/enzimologia , Fibroblastos/imunologia , Fibroblastos/metabolismo , Células HEK293 , Células HeLa , Humanos , Quinase I-kappa B/deficiência , MAP Quinase Quinase 4/antagonistas & inibidores , MAP Quinase Quinase 4/metabolismo , MAP Quinase Quinase 4/fisiologia , Camundongos , Camundongos Knockout , Subunidades Proteicas/deficiência , Transdução de Sinais/genética , Fator de Transcrição RelA/deficiência , Fator de Transcrição RelA/metabolismoRESUMO
Abs to acetylcholine receptor (AChR) and complement are the major constituents of pathogenic events causing neuromuscular junction destruction in both myasthenia gravis (MG) and experimental autoimmune MG (EAMG). To analyze the differential roles of the classical vs alternative complement pathways in EAMG induction, we immunized C3(-/-), C4(-/-), C3(+/-), and C4(+/-) mice and their control littermates (C3(+/+) and C4(+/+) mice) with AChR in CFA. C3(-/-) and C4(-/-) mice were resistant to disease, whereas mice heterozygous for C3 or C4 displayed intermediate susceptibility. Although C3(-/-) and C4(-/-) mice had anti-AChR Abs in their sera, anti-AChR IgG production by C3(-/-) mice was significantly suppressed. Both C3(-/-) and C4(-/-) mice had reduced levels of B cells and increased expression of apoptotis inducers (Fas ligand, CD69) and apoptotic cells in lymph nodes. Immunofluorescence studies showed that the neuromuscular junction of C3(-/-) and C4(-/-) mice lacked C3 or membrane attack complex deposits, despite having IgG deposits, thus providing in vivo evidence for the incapacity of anti-AChR IgGs to induce full-blown EAMG without the aid of complements. The data provide the first direct genetic evidence for the classical complement pathway in the induction of EAMG induced by AChR immunization. Accordingly, severe MG and other Ab- and complement-mediated diseases could be effectively treated by inhibiting C4, thus leaving the alternative complement pathway intact.