Zhou Yebin, Wu Jianming, Kucik Dennis F, White Nathan B, Redden David T, Szalai Alexander J, Bullard Daniel C, Edberg Jeffrey C
University of Alabama at, Birmingham.
Arthritis Rheum. 2013 Nov;65(11):2907-16. doi: 10.1002/art.38117.
Multiple studies have demonstrated that single-nucleotide polymorphisms (SNPs) in the ITGAM locus (including the nonsynonymous SNPs rs1143679, rs1143678, and rs1143683) are associated with systemic lupus erythematosus (SLE). ITGAM encodes the protein CD11b, a subunit of the β2 integrin Mac-1. The purpose of this study was to determine the effects of ITGAM genetic variation on the biologic functions of neutrophil Mac-1.
Neutrophils from ITGAM-genotyped and -sequenced healthy donors were isolated for functional studies. The phagocytic capacity of neutrophil ITGAM variants was probed with complement-coated erythrocytes, serum-treated zymosan, heat-treated zymosan, and IgG-coated erythrocytes. The adhesion capacity of ITGAM variants, in adhering to either purified intercellular adhesion molecule 1 or tumor necrosis factor α-stimulated endothelial cells, was assessed in a flow chamber. Expression levels of total CD11b and activation of CD11b were assessed by flow cytometry.
Mac-1-mediated neutrophil phagocytosis, determined in cultures with 2 different complement-coated particles, was significantly reduced in individuals with nonsynonymous variant alleles of ITGAM. This reduction in phagocytosis was related to variation at either rs1143679 (in the β-propeller region) or rs1143678/rs1143683 (highly linked SNPs in the cytoplasmic/calf-1 regions). Phagocytosis mediated by Fcγ receptors was also significantly reduced in donors with variant ITGAM alleles. Similarly, firm adhesion of neutrophils was significantly reduced in individuals with variant ITGAM alleles. These functional alterations were not attributable to differences in total receptor expression or activation.
The nonsynonymous ITGAM variants rs1143679 and rs1143678/rs113683 contribute to altered Mac-1 function on neutrophils. These results underscore the need to consider multiple nonsynonymous SNPs when assessing the functional consequences of ITGAM variation on immune cell processes and the risk of SLE.
多项研究表明，整合素α-M（ITGAM）基因座中的单核苷酸多态性（SNP）（包括非同义SNP rs1143679、rs1143678和rs1143683）与系统性红斑狼疮（SLE）相关。ITGAM编码蛋白CD11b，它是β2整合素Mac-1的一个亚基。本研究的目的是确定ITGAM基因变异对中性粒细胞Mac-1生物学功能的影响。
从经过ITGAM基因分型和测序的健康供体中分离出中性粒细胞用于功能研究。用补体包被的红细胞、血清处理的酵母聚糖、热处理的酵母聚糖和IgG包被的红细胞检测中性粒细胞ITGAM变异体的吞噬能力。在流动腔中评估ITGAM变异体与纯化的细胞间黏附分子1或肿瘤坏死因子α刺激的内皮细胞的黏附能力。通过流式细胞术评估总CD11b的表达水平和CD11b的激活情况。
在使用2种不同补体包被颗粒的培养物中测定的Mac-1介导的中性粒细胞吞噬作用，在具有ITGAM非同义变异等位基因的个体中显著降低。这种吞噬作用的降低与rs1143679（在β-螺旋桨区域）或rs1143678/rs1143683（细胞质/小牛-1区域中的高度连锁SNP）的变异有关。在具有变异ITGAM等位基因的供体中，由Fcγ受体介导的吞噬作用也显著降低。同样，具有变异ITGAM等位基因的个体中中性粒细胞的牢固黏附也显著降低。这些功能改变并非归因于总受体表达或激活的差异。
非同义ITGAM变异体rs1143679和rs1143678/rs113683导致中性粒细胞上Mac-1功能改变。这些结果强调在评估ITGAM变异对免疫细胞过程和SLE风险的功能影响时，需要考虑多个非同义SNP。
