CYTOSKELETAL AND MEMBRANE ASSOCIATIONS OF B-CELL IG

最近发表的实验表明，在B淋巴细胞中， 膜结合免疫球蛋白（mIg）与其他血浆 膜蛋白以及细胞骨架。 的目的 工作是阐明mIg相互作用的分子本质， 确定当mIg被交联或封端时它们是如何受到影响的 这是由于抗Ig试剂与B细胞表面结合。 最近我们 已经发现在鸡中至少有一些细胞免疫学相关的IG 是磷酸化的。 在非还原条件下，磷酸化的IG 一条轻链和一条重链的二聚体，仅重链 磷酸化。 虽然用抗Ig试剂交联mIg将连接 当额外的mIG连接到细胞骨架上时，新连接的IG不会成为 磷酸化 然而，交联mIg将触发 其他蛋白质的磷酸化。 特别是，具有分子量的蛋白质 130和38千道尔顿的重量似乎显示出增强的酪氨酸 在这些条件下的磷酸化。 这两种蛋白质都与 肌动蛋白，因此可能与细胞骨架有关。 他们的 磷酸化可以代表B细胞活化中的重要步骤。 在 我们的系统，即使是不与细胞骨架共分离的mIg， 通过二硫键与肌动蛋白结合，在表面上显示为 可能H2L2（肌动蛋白）2 与80的IG重链的复合物 千道尔顿。 然而，我们也发现了mIg存在于表面的证据 在具有IG重链的较大的二硫键连接结构中， 分子量为77千道尔顿。 77千道尔顿毫克重链可能 对于抗原结合更重要，因为 明显的高亲和力。 在这一点上，我们不知道的关系， 这种形式的免疫球蛋白与细胞骨架。 （一）

Recently published experiments suggest that in the B\lymphocyte, membrane-bound immunoglobulin (mIg) is associated with other plasma membrane proteins as well as with the cytoskeleton. The objective of this work is to elucidate the molecular nature of the mIg interactions and to determine how they are influenced when mIg is either cross-linked or capped as a result of anti-Ig reagents binding to B-cell surfaces. Recently, we have found that in the chicken at least some cytoskeletally-associated Ig is phosphorylated. Under non-reducing conditions, the phorphorylated Ig is a dimer of one light chain and one heavy chain, with only the heavy chain phosphorylated. While cross linking mIg with anti-Ig reagents will link additional mIg to the cytoskeleton, newly linked Ig does not become phosphorylated. However, cross linking mIg will trigger the phosphorylation of other proteins. In particular, proteins with molecular weights of 130 and 38 kilodaltons appear to show enhanced tryosine phosphorylation under these conditions. Both of these proteins bind to actin and so may be associated with the cytoskeleton. Their phosphorylation may represent a significant step in B-cell activation. In our system, even mIg that does not co-isolate with the cytoskeleton may be bound to actin via disulphide linkages, appearing on the surface as possible H2L2(actin)2 complexes with an Ig heavy chain of 80 kilodaltons. However, we also find evidence for mIg present on the surface in larger disulphide-linked structures with Ig heavy chains, all with a molecular weight of 77 kilodaltons. The 77 kilodalton mIg heavy chain may be the more significant with respect to antigen binding because of an apparent high avidity. At this point, we do not know the relationship of this form of mIg with the cytoskeleton. (I)