RESUMO
The human B cell restricted activation antigen B7 identifies an in vivo primed subpopulation of B cells that demonstrate an accelerated response to triggers of B cell activation and proliferation. The cDNA encoding B7 was molecularly cloned by cDNA expression. The identity of the B7 cDNA was confirmed by indirect immunofluorescence and immunoprecipitation of a 44/54-kDa protein from B7 transfected COS cells. The sequence of the B7 polypeptide predicts a type I membrane protein of 262 amino acids with eight potential N-linked glycosylation sites in the extracellular region and a short, highly positively charged cytoplasmic tail. The extracellular region is homologous to the Ig gene superfamily and consists of two contiguous Ig-like domains. The first Ig domain has the characteristics of a variable domain and the second that of a constant region domain. B7 mRNA was detected only on anti-Ig activated B lymphocytes and not in other hematopoietic cells. After in vitro activation of B cells with anti-Ig, B7 mRNA was maximally expressed between 4 and 12 h with four RNA transcripts of 1.7, 2.9, 4.2, and 10 kb. The 2.9-kb mRNA predominated in in vitro-activated B cells whereas the 1.7-kb mRNA was most abundant in tumor cells of B cell origin. B7 expression was confined to several histologically defined subgroups of B cell malignancies. The majority of non-Hodgkin's lymphomas were B7+ whereas the B cell leukemias and circulating non-Hodgkin's lymphomas were generally negative. These results demonstrate that the B7 gene encodes a unique molecule belonging to the Ig superfamily and that B7 expression is limited to normal activated B cells and noncirculating B cell malignancies.
Assuntos
Antígenos de Diferenciação de Linfócitos B/isolamento & purificação , Linfócitos B/análise , Ativação Linfocitária , Células Tumorais Cultivadas/análise , Sequência de Aminoácidos , Antígenos de Diferenciação de Linfócitos B/genética , Linfócitos B/imunologia , Sequência de Bases , Southern Blotting , Linhagem Celular , Clonagem Molecular , DNA/isolamento & purificação , Genes Neoplásicos , Células-Tronco Hematopoéticas/análise , Humanos , Dados de Sequência Molecular , Família Multigênica , RNA Mensageiro/isolamento & purificação , Homologia de Sequência do Ácido Nucleico , Transfecção , Células Tumorais Cultivadas/imunologiaRESUMO
In the present report we demonstrate that the IL-6 gene is expressed in anti-Ig-activated and neoplastic B cells. After activation with anti-Ig, splenic B cells rapidly expressed IL-6 mRNA with peak expression occurring at 4 h and declining rapidly thereafter. In an attempt to exclude that the IL-6 mRNA expression was in non-B cells, T cells and monocytes were extensively depleted. In this highly purified B cell population, IL-6 mRNA was retained, whereas the expression of the T cell- and monocyte-restricted CD2 and CD14 genes was nearly undetectable. These results are consistent with the conclusion that activated B cells express IL-6 mRNA. Because we found IL-6 mRNA expression in normal activated B lymphocytes, we examined the expression of IL-6 mRNA in B cell neoplasms. 11 of 25 non-Hodgkins B cell lymphomas and 4 of 4 myelomas and plasma cell leukemias expressed IL-6 mRNA, whereas only 1 of 19 B cell leukemias was positive. To exclude that IL-6 mRNA expression in neoplastic B cells was the result of contaminating non-B cells, T cells and monocytes were extensively depleted from the tumor specimens. In the three IL-6-positive tumor samples depleted of T cells and monocytes, IL-6 mRNA expression was retained in all cases. These observations provide support for the idea that the IL-6 gene is expressed in normal activated and neoplastic B cells.
