Kumar A, Kumar P, Schur P H
Department of Rheumatology/Immunology, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
Clin Immunol Immunopathol. 1991 Jul;60(1):55-64. doi: 10.1016/0090-1229(91)90111-m.
The molecular basis of complement component C4A deficiency in white U.S. and Mexican patients with systemic lupus erythematosus (SLE) was studied. Genomic DNA from SLE patients and non-SLE controls was analyzed for restriction fragments using HindIII and a 5' C4 cDNA probe. C4A gene deletion was recognized by the loss of a 15-kb restriction fragment and the appearance of a 8.5-kb fragment. Thirty-two selected U.S. SLE patients, 7 nonSLE controls, and 11 Mexican SLE patients and 9 relatives were studied. The deletion was recognized in all of the 14 HLA-B8;DR3 SLE patients with a C4A protein deficiency. Two SLE patients with DR3 but without B8 also had this gene deletion. None of the 3 U.S. SLE nonDR3, C4A protein deficient patients nor 20 C4A protein deficient Mexican individuals (11 SLE patients and 9 relatives; none had B8 and/or DR3) showed this deletion. Thus the C4A gene deletion failed to account for the C4A protein deficiency in all the nonDR3 Mexicans and in some U.S. SLE patients. To determine whether gene conversion at the C4A locus would encode a C4B-like protein and be responsible for the C4A protein deficiency (in nonDR3 patients), the C4d region of the gene was amplified by polymerase chain reaction and subjected to Nla IV digestion, and restriction fragment analysis was performed using a C4d region-specific probe. The resulting restriction fragment length polymorphism pattern revealed no changes in the isotype-specific region of the gene as characterized by C4A-specific 276- and 191-bp fragments in Dr3 or nonDR3 individuals. Thus, homoexpression of C4B at both loci was not responsible for C4A deficiency in nonDR3 SLE patients without C4A gene deletion.
对美国白人和墨西哥系统性红斑狼疮（SLE）患者补体成分C4A缺乏的分子基础进行了研究。使用HindIII和5' C4 cDNA探针分析SLE患者和非SLE对照的基因组DNA的限制性片段。通过15kb限制性片段的缺失和8.5kb片段的出现来识别C4A基因缺失。研究了32名选定的美国SLE患者、7名非SLE对照、11名墨西哥SLE患者和9名亲属。在所有14名HLA - B8;DR3且C4A蛋白缺乏的SLE患者中均识别出该缺失。两名有DR3但无B8的SLE患者也有此基因缺失。3名美国非DR3、C4A蛋白缺乏的SLE患者以及20名C4A蛋白缺乏的墨西哥个体（11名SLE患者和9名亲属；均无B8和/或DR3）均未显示该缺失。因此，C4A基因缺失无法解释所有非DR3墨西哥人和一些美国SLE患者中的C4A蛋白缺乏。为了确定C4A基因座处的基因转换是否会编码一种类似C4B的蛋白并导致（非DR3患者中的）C4A蛋白缺乏，通过聚合酶链反应扩增该基因的C4d区域并进行Nla IV消化，然后使用C4d区域特异性探针进行限制性片段分析。所得的限制性片段长度多态性模式显示该基因的同种型特异性区域没有变化，在DR3或非DR3个体中以C4A特异性的276bp和191bp片段为特征。因此，两个基因座处C4B的同源表达不是无C4A基因缺失的非DR3 SLE患者中C4A缺乏的原因。
