Lee Wen-I, Zhu Quli, Gambineri Eleonora, Jin YinZhu, Welcher Andrew A, Ochs Hans D
School of Medicine, University of Washington, Seattle 98195-6320, USA.
J Allergy Clin Immunol. 2003 Nov;112(5):958-64. doi: 10.1016/s0091-6749(03)02021-9.
Inducible CO-stimulatory molecule (ICOS), the third member of the CD28/CTLA4 family, is expressed by activated T cells and interacts with its ligand (ICOSL, B7-related protein-1 [B7RP-1]) that is constitutively expressed by B cells. The interaction of ICOS with its ligand leads to terminal differentiation of B cells to plasma cells. ICOS-deficient mice fail to undergo immunoglobulin-class switch recombination (CSR) and germinal center formation, suggesting that ICOS could be a candidate gene for phenotypic hyper-IgM (HIGM) syndromes characterized by recurrent infections, low serum IgG and IgA, and normal or elevated IgM. Genetically, at least 4 distinct molecular defects have been identified that result in defective CSR and present as HIGM syndromes: defects of the CD40 ligand gene (CD40L; HIGM1, X-linked), the activation-induced cytidine deaminase gene (AID; HIGM2, autosomal recessive), the CD40 gene (HIGM3, autosomal recessive), and the nuclear factor-kappaB (NF-kappaB) essential modulator gene (NEMO, or IKK-gamma, X-linked). In a substantial subgroup of HIGM patients, these 4 genes are normal, and the genetic defect is unknown.
We sought to investigate the possibility that mutations of ICOS could account for some patients' belonging to this HIGM subgroup.
The expression of ICOS protein by activated peripheral blood mononuclear cells and/or interleukin-2-dependent T cell lines derived from these patients was estimated by flow cytometery after incubation of the cells with the ICOS ligand fusion protein B7RP-1 Fc. The coding region and exon-intron boundaries of ICOS were assessed by sequence analysis.
We studied 33 HIGM patients from 30 families, selected from an original cohort of 136 patients from 113 families, by excluding mutations of CD40L, AID, CD40, and NEMO. Activated T cells from all 33 patients expressed ICOS normally, and sequence analysis of the coding region and exon-intron boundaries revealed only wild-type ICOS, predicting that the protein structure is normal in this patient population.
These findings strongly suggest that ICOS does not belong to the group of genes that, if mutated, present clinically as the HIGM syndrome.
诱导性共刺激分子（ICOS）是CD28/CTLA4家族的第三个成员，由活化的T细胞表达，并与其配体（ICOS配体，B7相关蛋白-1 [B7RP-1]）相互作用，B7RP-1由B细胞组成性表达。ICOS与其配体的相互作用导致B细胞终末分化为浆细胞。ICOS缺陷小鼠无法进行免疫球蛋白类别转换重组（CSR）和生发中心形成，这表明ICOS可能是表型高IgM（HIGM）综合征的候选基因，该综合征的特征为反复感染、血清IgG和IgA水平低，以及IgM正常或升高。在遗传学上，已鉴定出至少4种不同的分子缺陷，这些缺陷导致CSR缺陷并表现为HIGM综合征：CD40配体基因（CD40L；HIGM1，X连锁）缺陷、活化诱导的胞苷脱氨酶基因（AID；HIGM2，常染色体隐性遗传）缺陷、CD40基因（HIGM3，常染色体隐性遗传）缺陷以及核因子-κB（NF-κB）必需调节基因（NEMO，或IKK-γ，X连锁）缺陷。在相当一部分HIGM患者亚组中，这4个基因是正常的，遗传缺陷尚不清楚。
我们试图研究ICOS突变是否可能是导致某些患者属于该HIGM亚组的原因。
用ICOS配体融合蛋白B7RP-1 Fc孵育细胞后，通过流式细胞术评估这些患者外周血活化单核细胞和/或白细胞介素-2依赖T细胞系中ICOS蛋白的表达。通过序列分析评估ICOS的编码区和外显子-内含子边界。
我们从最初的113个家庭的136名患者队列中筛选出30个家庭的33名HIGM患者，排除了CD40L、AID、CD40和NEMO的突变。所有33名患者的活化T细胞均正常表达ICOS，编码区和外显子-内含子边界的序列分析仅显示野生型ICOS，这表明该患者群体中ICOS的蛋白质结构正常。
这些发现强烈表明，ICOS不属于那些发生突变后临床上表现为HIGM综合征的基因。
