RESUMO
To elucidate the function of the two cytokine-binding modules (CBM) of the leukemia inhibitory factor receptor (LIFR), receptor chimeras of LIFR and the interleukin-6 receptor (IL-6R) were constructed. Either the NH(2)-terminal (chimera RILLIFdeltaI) or the COOH-terminal LIFR CBM (chimera RILLIFdeltaII) were replaced by the structurally related CBM of the IL-6R which does not bind LIF. Chimera RILLIFdeltaI is functionally inactive, whereas RILLIFdeltaII binds LIF and mediates signalling as efficiently as the wild-type LIFR. Deletion mutants of the LIFR revealed that both the NH(2)-terminal CBM and the Ig-like domain of the LIFR are involved in LIF binding, presumably via the LIF site III epitope. The main function of the COOH-terminal CBM of the LIFR is to position the NH(2)-terminal CBM and the Ig-like domain, so that these can bind to LIF. In analogy to a recently published model of the IL-6R complex, a model of the active LIFR complex is suggested which positions the COOH-terminal CBM at LIF site I and the NH(2)-terminal CBM and the Ig-like domain at site III. An additional contact is postulated between the Ig-like domain of gp130 and the NH(2)-terminal CBM of the LIFR.
Assuntos
Inibidores do Crescimento/metabolismo , Imunoglobulinas/química , Interleucina-6 , Linfocinas/metabolismo , Receptores de Citocinas/química , Receptores de Citocinas/metabolismo , Substituição de Aminoácidos/genética , Animais , Sítios de Ligação , Células COS , Divisão Celular/efeitos dos fármacos , Linhagem Celular , Inibidores do Crescimento/farmacologia , Humanos , Fator Inibidor de Leucemia , Subunidade alfa de Receptor de Fator Inibidor de Leucemia , Ligantes , Linfocinas/farmacologia , Oncostatina M , Peptídeos/metabolismo , Fosforilação , Fosfotirosina/metabolismo , Estrutura Terciária de Proteína , Receptores de Citocinas/genética , Receptores de Interleucina-6/química , Receptores de Interleucina-6/genética , Receptores de Interleucina-6/metabolismo , Receptores de OSM-LIF , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Deleção de Sequência/genética , TransfecçãoRESUMO
In spite of thymic involution early in life, the numbers of naive CD4(+) T cells only slowly decline in ageing humans implying peripheral post-thymic naive CD4(+) T cell expansion. This proliferation may compensate for continuous activation and death of naive CD4(+) T cells but may also have negative consequences for protective immunity. Here we show that naive CD4(+) T cells that have proliferated in the periphery are characterized by a highly restricted oligoclonal TCR repertoire. Additionally these cells, which constitute the majority of naive CD4(+) T cells in the elderly, display signatures of recent TCR engagement. Our results demonstrate for the first time that peripheral post-thymic proliferation of naive CD4(+) T cells in healthy human individuals causes a significant contraction of the peripheral TCR repertoire. This age-dependent deterioration of CD4(+) T cell immunity could entail ageing-associated autoimmunity, increased susceptibility to infection or cancer and decreased efficiency of vaccination.