Tamma S M, Amin A R, Finkelman F D, Chen Y W, Thorbecke G J, Coico R F
Department of Microbiology, City University of New York Medical School, NY 10031.
Proc Natl Acad Sci U S A. 1991 Oct 15;88(20):9233-7. doi: 10.1073/pnas.88.20.9233.
Receptors for immunoglobulins on animal cells invariably show specificity for Fc regions of the protein and are hence called Fc receptors. The present study shows that immunoglobulin D receptors present an exception to this rule. Binding of IgD-coated erythrocytes to murine IgD-receptor-bearing T-helper cells is competitively inhibited by IgD, by its Fab delta fragments, and by deletion mutants of IgD lacking (i) the first constant domain of the delta heavy chain (KWD1), (ii) that region plus the delta heavy-chain-hinge region (KWD6), or (iii) the third constant domain of the delta heavy chain (Gen. 24). KWD1, Gen. 24, or KWD6 mutants bind to T-helper cells bearing receptors for IgD independently of each other. Furthermore, Gen. 24 and KWD6 mutants also competitively inhibit binding of each other in cross-blocking experiments. These results show that the IgD receptors binds to the Fd delta and the Fc delta and cannot readily be explained by sequence homology between the two parts of the IgD molecule.
动物细胞上的免疫球蛋白受体总是对该蛋白质的Fc区域表现出特异性，因此被称为Fc受体。本研究表明，免疫球蛋白D受体是这一规律的例外。包被IgD的红细胞与带有鼠IgD受体的辅助性T细胞的结合受到IgD、其Fabδ片段以及缺乏（i）δ重链的第一个恒定结构域（KWD1）、（ii）该区域加上δ重链铰链区（KWD6）或（iii）δ重链的第三个恒定结构域（Gen. 24）的IgD缺失突变体的竞争性抑制。KWD1、Gen. 24或KWD6突变体彼此独立地与带有IgD受体的辅助性T细胞结合。此外，在交叉阻断实验中，Gen. 24和KWD6突变体也相互竞争性抑制结合。这些结果表明，IgD受体与Fdδ和Fcδ结合，并且不能轻易地用IgD分子这两部分之间的序列同源性来解释。
