Neutralization of hepatitis A virus (HAV) by an immunoadhesin containing the cysteine-rich region of HAV cellular receptor-1

Hepatitis A virus (HAV) infects African green monkey kidney (AGR IK) cells via the HAV cellular receptor-1 (havcr-1), a mucin-like type 1 integral-mem brane glycoprotein of unknown natural function. The ectodomain of havcr-1 c ontains an N-terminal immunoglobulin-like cysteine-rich region (D1), which binds protective monoclonal antibody (MAb) 190/4, followed by an O-glycosyl ated mucin-like threonine-serine-proline-rich region that extends D1 well a bove the cell surface. To study the interaction of HAV with havcr-1, we con structed immunoadhesins fusing the hinge and Fc portion of human IgG1 to D1 (D1-Fc) or the ectodomain of the poliovirus receptor (PVR-Fc) and expresse d them in CHO cells. These immunoadhesins,were secreted to the cell culture medium and purified through protein A-agarose columns. In a solid-phase as say, HAV bound to D1-Fc in a concentration-dependent manner whereas backgro und levels of HAV bound to PVR-Fc. Binding of HAV to D1-Fc was blocked by t reatment with MAb 190/4 but not with control MAb, M2, which binds to a tag epitope introduced between the D1 and Fe portions of the immunoadhesin. D1- Fc neutralized approximately 1 log unit of the HAV infectivity in AGMK cell s, whereas PVR-Fc had no effect in the HAV titers. A similarly poor reducti on in HAV titers was observed after treating the same stock of HAV with mur ine neutralizing MAbs K2-4F2, K3-4C8, and VHA 813. Neutralization of poliov irus by PVR-Fc but not by D1-Fc indicated that the virus-receptor interacti ons were specific. These results show that D1 is sufficient for binding and neutralization of HAV and provide further evidence that havcr-1 is a funct ional cellular receptor for HAV.