Kumpel B M, van de Winkel J G, Westerdaal N A, Hadley A G, Dugoujon J M, Blancher A
International Blood Group Reference Laboratory, Bristol, U.K.
Br J Haematol. 1996 Jul;94(1):175-83. doi: 10.1046/j.1365-2141.1996.d01-1764.x.
IgG antibodies to the Rh D polypeptide on red cells are normally IgG1 or IgG3, whereas antibodies produced in response to carbohydrate antigens such as the A and B blood groups are predominantly IgG2. The consequences of this isotype restriction for the immune destruction of red cells were investigated. Human IgG2 anti-D and IgG2 anti-A were isolated by affinity purification from an unusual anti-D serum (DEL) and anti-A sera, respectively. These antibodies were compared with IgG1 and IgG3 monoclonal anti-D in in vitro functional assays of the interaction between IgG-coated red cells (EA-IgG) and cells bearing IgG Fc receptors (Fc gamma R). Dimeric IgG2 anti-D bound efficiently to cell lines transfected with Fc gamma RIIa-H131, an allotypic form of Fc gamma RIIa which readily interacts with IgG2, IgG1 and IgG3. Unexpectedly, however, -D- phenotype red cells coated with IgG2 anti-D did not form rosettes with these cells, whereas EA-IgG2 anti-A and EA-IgG1 and EA-IgG3 anti-D effectively formed rosettes with these transfectants at the same sensitization level (100,000 molecules IgG/red cell). In antibody-dependent cell-mediated cytotoxicity (ADCC) assays, lysis of EA-IgG2 anti-A was mediated via Fc gamma RIIa, whereas lysis of EA-IgG1 and EA-IgG3 anti-D was mediated via Fc gamma RI or Fc gamma RIII; EA-IgG2 anti-D was inactive in all functional assays. These experiments suggest that both IgG subclass and antigen structure affect functional IgG-Fc gamma R interactions. The topography of the Rh D antigen, an integral membrane protein, ensures that anti-D is bound near the lipid bilayer surrounded by the glycocalyx. This may sterically hinder access of Fc gamma RIIa-H131 to the Fc gamma R recognition site on the relatively inflexible IgG2 anti-D, but not to that of IgG1 or IgG3 anti-D. In contrast, IgG2 bound to the A antigen on glycoproteins is not so constrained. The topography of the D and A antigens may thus determine whether functional interactions of red-cell-bound IgG2 anti-D and IgG2 anti-A with cells bearing Fc gamma receptors can occur.
针对红细胞上Rh D多肽的IgG抗体通常为IgG1或IgG3，而针对碳水化合物抗原（如A和B血型抗原）产生的抗体主要是IgG2。研究了这种同种型限制对红细胞免疫破坏的影响。通过亲和纯化分别从不寻常的抗-D血清（DEL）和抗-A血清中分离出人IgG2抗-D和IgG2抗-A。在IgG包被的红细胞（EA-IgG）与带有IgG Fc受体（FcγR）的细胞之间相互作用的体外功能试验中，将这些抗体与IgG1和IgG3单克隆抗-D进行比较。二聚体IgG2抗-D能有效地与转染了FcγRIIa-H131（FcγRIIa的一种同种异型形式，能轻易与IgG2、IgG1和IgG3相互作用）的细胞系结合。然而，出乎意料的是，用IgG2抗-D包被的-D-表型红细胞不能与这些细胞形成玫瑰花结，而EA-IgG2抗-A以及EA-IgG1和EA-IgG3抗-D在相同致敏水平（100,000个IgG分子/红细胞）下能有效地与这些转染细胞形成玫瑰花结。在抗体依赖性细胞介导的细胞毒性（ADCC）试验中，EA-IgG2抗-A的裂解是通过FcγRIIa介导的，而EA-IgG1和EA-IgG3抗-D的裂解是通过FcγRI或FcγRIII介导的；EA-IgG2抗-D在所有功能试验中均无活性。这些实验表明，IgG亚类和抗原结构都会影响功能性IgG-FcγR相互作用。Rh D抗原是一种整合膜蛋白，其拓扑结构确保抗-D在糖萼包围的脂质双层附近结合。这可能在空间上阻碍FcγRIIa-H131接近相对刚性的IgG2抗-D上的FcγR识别位点，但不会阻碍其接近IgG1或IgG3抗-D的识别位点。相比之下，与糖蛋白上A抗原结合的IgG2没有受到如此限制。因此，D和A抗原的拓扑结构可能决定红细胞结合的IgG2抗-D和IgG2抗-A与带有Fcγ受体的细胞之间是否能发生功能性相互作用。
