Yoden S, Kida H, Yanagawa R
Arch Virol. 1985;85(3-4):209-16. doi: 10.1007/BF01314232.
Biological activities of Fab fragments of monoclonal IgG antibodies to each of four nonoverlapping antigenic areas on the hemagglutinin molecule of A/seal/Massachusetts/1/80 (H7N7) influenza virus were examined. Fab fragments of the antibodies belonging to groups I and II neutralized viral infectivity. These Fab fragments inhibited hemagglutination of the virus and virus-induced hemolysis at pH 5.9. On the other hand, Fab fragments of groups III and IV antibodies showed neither neutralization nor hemolysis-inhibition activities, while intact IgG molecules of groups III and IV effectively neutralized viral infectivity and inhibited virus-induced hemolysis, as previously found. These IgG molecules scarcely or did not inhibit hemagglutination of the virus. Neutralization of viral infectivity, however, was observed when the virus was coated with Fab fragments of groups III and IV antibodies and then incubated with anti-Fab fragment antibodies. These findings suggest that bivalent binding of the IgG antibodies of groups III and IV is required for neutralization of viral infectivity through a proposed mechanism by which these antibodies interfere with a low pH-induced conformational change resulting in inhibition of the fusion step of the viral replication process.
检测了针对A/海豹/马萨诸塞/1/80（H7N7）流感病毒血凝素分子上四个不重叠抗原区域的单克隆IgG抗体Fab片段的生物学活性。I组和II组抗体的Fab片段中和了病毒感染性。这些Fab片段在pH 5.9时抑制了病毒的血凝作用和病毒诱导的溶血。另一方面，III组和IV组抗体的Fab片段既没有中和活性也没有溶血抑制活性，而III组和IV组的完整IgG分子如先前发现的那样有效地中和了病毒感染性并抑制了病毒诱导的溶血。这些IgG分子几乎不抑制或不抑制病毒的血凝作用。然而，当病毒用III组和IV组抗体的Fab片段包被，然后与抗Fab片段抗体孵育时，观察到了病毒感染性的中和。这些发现表明，III组和IV组IgG抗体的二价结合是通过一种推测的机制中和病毒感染性所必需的，在该机制中，这些抗体干扰低pH诱导的构象变化，从而抑制病毒复制过程的融合步骤。
