Nikolova E B, Tomana M, Russell M W
Department of Microbiology, University of Alabama at Birmingham 35294.
Immunology. 1994 Jun;82(2):321-7.
In contrast to antigen-antibody complexes containing native human IgA, solid-phase-deposited IgA activates the alternative complement pathway and binds C3b. To investigate the role of carbohydrate chains in this, various human IgA preparations were treated with neuraminidase alone or together with N-glycanase or O-glycanase, or with mixed glycosidases from the oral bacterium, Streptococcus mitis. Depletion of oligosaccharides was determined by carbohydrate analysis. Removal of sialic acid and N-linked glycan chains greatly increased the C3b-fixing properties of normal serum IgA1 and IgA2. Myeloma IgA1 and IgA2 proteins and secretory IgA had higher C3b-binding activity than normal serum IgA, and this was further increased by removal of sialic acid and N-linked glycans. Fc alpha and Fc alpha-SC fragments of myeloma and secretory IgA1, respectively, but not Fab alpha fragments, obtained by cleavage with bacterial IgA1 proteases and also free secretory component, fixed C3b by the alternative pathway.
与含有天然人IgA的抗原-抗体复合物不同，固相沉积的IgA激活替代补体途径并结合C3b。为了研究碳水化合物链在此过程中的作用，使用神经氨酸酶单独或与N-糖苷酶或O-糖苷酶一起，或用口腔细菌缓症链球菌的混合糖苷酶处理各种人IgA制剂。通过碳水化合物分析确定寡糖的消耗情况。去除唾液酸和N-连接聚糖链极大地增加了正常血清IgA1和IgA2的C3b结合特性。骨髓瘤IgA1和IgA2蛋白以及分泌型IgA比正常血清IgA具有更高的C3b结合活性，去除唾液酸和N-连接聚糖后，这种活性进一步增加。通过用细菌IgA1蛋白酶切割分别获得的骨髓瘤和分泌型IgA1的Fcα和Fcα-SC片段，但不是Fabα片段，以及游离的分泌成分，通过替代途径固定C3b。
