Role for β2-Microglobulin in Echovirus Infection of Rhabdomyosarcoma Cells

A monoclonal antibody (MAb) that blocks most echoviruses (EVs) from infecting rhabdomyosarcoma (RD) cells has been isolated. By using the CELICS cloning method (T. Ward, P. A. Pipkin, N. A. Clarkson, D. M. Stone, P. D. Minor, and J. W. Almond, EMBO J. 13:5070–5074, 1994), the ligand for this antibody has been identified as β2-microglobulin (β2m), the 12-kDa protein that associates with class I heavy chains to form class I HLA complexes. A commercial MAb (MAb 1350) against β2m was also found to block EV7 infection without affecting binding to its receptor, DAF, or replication of EV7 viral RNA inside cells. Entry of EV7 into cells was reduced by only 30% by antibody and cytochalasin D, an inhibitor of endocytosis mediated by caveolae and clathrin-coated pits, but was not significantly reduced by sodium azide. The block to virus entry by cytochalasin D was additive to the block induced by antibody. We suggest that EV7 rapidly enters into a multicomponent receptor complex prior to entry into cells and that this initial entry event requires β2m or class I HLA for infection to proceed.

本研究成功分离出一株可阻断绝大多数埃可病毒（echoviruses, EVs）感染横纹肌肉瘤（rhabdomyosarcoma, RD）细胞的单克隆抗体（monoclonal antibody, MAb）。通过CELICS克隆法（CELICS cloning method，参考文献：T. Ward、P. A. Pipkin、N. A. Clarkson、D. M. Stone、P. D. Minor及J. W. Almond，《EMBO J.》1994年，第13卷，第5070–5074页），研究人员鉴定出该抗体的配体为β2微球蛋白（β2-microglobulin, β2m）——一种分子量为12 kDa的蛋白，可与I类重链结合形成I类人类白细胞抗原复合物（class I HLA complexes）。一款商用抗β2m单克隆抗体（MAb 1350）同样被发现可阻断EV7感染，且不会影响病毒与其受体衰变加速因子（DAF）的结合，也不会干扰细胞内EV7病毒RNA的复制。实验结果显示，抗体与细胞松弛素D（cytochalasin D，一种可阻断陷窝蛋白及网格蛋白包被小泡介导的内吞作用的抑制剂）联合处理时，仅能使EV7的细胞入侵效率降低30%；而叠氮钠（sodium azide）未对病毒入侵产生显著抑制效果。细胞松弛素D介导的病毒入侵阻断与抗体诱导的阻断作用呈相加效应。据此，研究团队提出推测：EV7在完成细胞入侵前会快速组装多组分受体复合物，且该初始入侵事件需要β2m或I类人类白细胞抗原复合物的参与，才能顺利完成感染进程。