Schultz D R, Arnold P I
Department of Medicine, University of Miami School of Medicine, Florida.
Immunobiology. 1992 Jun;185(1):90-102. doi: 10.1016/S0171-2985(11)80320-7.
The fourth component of human complement (C4) is encoded at two separate but closely linked loci within the MHC on the short arm of chromosome 6. Thus, there are two types of C4 protein in most individual and pooled normal human sera (NHS): C4A and C4B. Incubation of individual sera, pooled NHS, or purified heterogeneous C4 (C4A/C4B) with bacterial sialidase at 37 degrees C increased C-mediated hemolysis of antibody-sensitized sheep erythrocytes 1.54- to 1.93-fold. Comparative studies of Tmax of human C2, using asialo-C4 or buffer-treated C4 on EAC1gp and extrapolation to time 0 indicated a z value 4-fold higher with asialo-C4. This indicated that more hemolytically active C42 complexes are available with sialidase-treated C4 compared to untreated C4. There was no appreciable difference in the % 125I-C4 bound to EAC1gp (sialidase- or buffer-treated). Sera from two different blood donors with C4A3 phenotype (C4BQ0), two different donors with C4B1 phenotype (C4AQ0), and serum from an individual heterozygous deficient at both C4A3 and C4B1 regions (A3, AQ0; B1, BQ0) were investigated. The C4 allotypes, purified from these sera, were treated with sialidase; the C4A3 was enhanced in hemolytic assays by sialidase-treatment (1.52- to 2.3-fold), whereas the C4B1 allotype was not enhanced. Fluorometric determinations revealed that approximately the same percentage of sialic acid was released from sialidase-treated C4A3 and C4B1. Therefore, the increase in hemolytic titer observed after treatment of NHS or purified heterogeneous C4 with sialidase is a property of C4A3 but not a property of C4B1.
人类补体的第四成分（C4）由位于6号染色体短臂上主要组织相容性复合体（MHC）内两个独立但紧密连锁的基因座编码。因此，在大多数个体血清和混合正常人血清（NHS）中存在两种类型的C4蛋白：C4A和C4B。将个体血清、混合NHS或纯化的异质性C4（C4A/C4B）与细菌唾液酸酶在37℃孵育，可使C介导的抗体致敏绵羊红细胞的溶血增加1.54至1.93倍。使用脱唾液酸C4或缓冲液处理的C4对EAC1gp上的人C2的Tmax进行比较研究，并外推至时间0，结果表明脱唾液酸C4的z值高4倍。这表明与未处理的C4相比，唾液酸酶处理的C4可产生更多具有溶血活性的C42复合物。与EAC1gp结合的125I-C4（唾液酸酶处理或缓冲液处理）百分比没有明显差异。研究了来自两名具有C4A3表型（C4BQ0）的不同献血者的血清、两名具有C4B1表型（C4AQ0）的不同献血者的血清以及一名在C4A3和C4B1区域均杂合缺陷（A3，AQ0；B1，BQ0）个体的血清。从这些血清中纯化的C4同种异型用唾液酸酶处理；唾液酸酶处理可增强C4A3在溶血试验中的活性（1.52至2.3倍），而C4B1同种异型则未增强。荧光测定显示，唾液酸酶处理的C4A3和C4B1释放的唾液酸百分比大致相同。因此，用唾液酸酶处理NHS或纯化的异质性C4后观察到的溶血效价增加是C4A3的特性，而不是C4B1的特性。
