Kinetic events involved in immunotoxin-antigen binding and intracellular trafficking.

Each yellow arrow indicates a kinetic step of the model. The tumor cell sheds the surface antigen and the surface complexed antigen at a certain rate. The immunotoxin molecule exiting from the capillary diffuses in the extra-cellular space and binds to either the surface antigen or shed antigen by the association reaction between the antigen and immunotoxin. The surface-bound immunotoxin is internalized by the receptor-mediated endocytosis and mostly inactivated in the endosomal stage. The surviving toxin translocates to the cytosol, where the toxin inhibits protein synthesis and eventually causes cell death. In non-intoxicated cells, the antigen is replenished by fresh protein synthesis.

本模型中每个黄色箭头均代表一个动力学步骤。肿瘤细胞以特定速率脱落其表面抗原（surface antigen）及表面复合抗原（surface complexed antigen）。从毛细血管渗出的免疫毒素（immunotoxin）分子可在细胞外间隙（extracellular space）中扩散，并通过抗原与免疫毒素之间的结合反应，与表面抗原或脱落抗原相结合。结合于细胞表面的免疫毒素可通过受体介导的内吞作用（receptor-mediated endocytosis）被摄入细胞，并大多在内体阶段（endosomal stage）失活。存活下来的毒素可转位至胞浆（cytosol），在此处抑制蛋白质合成并最终导致细胞死亡。未受毒素作用的细胞可通过新生蛋白质合成补充抗原储备。