Immunoglobulin subclasses: roles in activity of IGIV and

总结：为了确定IgG亚类在中和HIV-1的能力上是否不同，将多克隆HIVIG通过蛋白A柱，收集适当的级分，并显示纯度> 89%的IgG 1、IgG 2和IgG 3（IgG 4的存在量不足以进行研究）。所有三个亚类均显示与所有主要HIV-1蛋白结合（IgG 1> IgG 2> IgG 3）。 与此相反，IgG 3在其中和HIV-1的能力方面比其他亚类更有活性，如通过合胞体抑制和无细胞病毒中和所测定的（IgG 3> IgG 1> IgG 2）。HIVIG及其亚类中和病毒的能力也取决于病毒株，因此嗜T细胞（R4）比嗜巨噬细胞（R5）病毒更敏感。IgG 3与IgG 1和IgG 2的不同之处在于铰链区更长且更柔性。 为了测试这在中和病毒中是否重要，用木瓜蛋白酶将IgG级分消化成Fc和Fab片段，并测试Fab片段的活性。 铰链区存在于F（ab）2中，但不存在于Fab片段中。当与来自其它IgG亚类的F（ab）2片段相比时，来自IgG 3的F（ab）2片段而不是Fab片段保留了它们的上级中和HIV-1的能力，表明IgG 3的较长铰链区使得IgG 3能够更有效地中和HIV-1。这些发现对HIVIG的生产和临床应用具有重要意义，特别是因为IgG 3比其他同种型更易受蛋白水解酶的影响。 此外，他们建议HIV-1疫苗应诱导高滴度IgG 3应答。

Summary: To determine whether IgG subclasses differ in their ability to neutralize HIV-1, polyclonal HIVIG was passed over protein A columns and the appropriate fractions collected and shown to be > 89% pure IgG1, IgG2 and IgG3 (IgG4 was not present in sufficient quantities for study). All three subclasses showed binding to all major HIV-1 proteins (IgG1 >IgG2 > IgG3). In contrast, IgG3 was more active than other subclasses in its ability to neutralize HIV-1 as assayed by syncytia inhibition and cell-free virus neutralization (IgG3 > IgG1 > IgG2). The ability of HIVIG and the subclasses to neutralize viruses also depended on the virus strain, so that T cell tropic (R4) were more susceptible than Macrophage tropic (R5) viruses. IgG3 differs from IgG1 and IgG2 by virtue of a longer and more flexible hinge region. To test whether this is important in neutralizing virus, the IgG fractions were digested by papain into Fc and Fab fragments and the Fab fragments tested for activity. The hinge region is present in the F(ab)2, but not in the Fab fragments. F(ab)2, but not Fab, fragments from IgG3, retained their superior ability to neutralize HIV-1 when compared to F(ab)2 fragments from other IgG subclasses, indicating that the longer hinge region of IgG3 enables IgG3 to neutralize HIV-1 more efficiently. These findings have implications for manufacture and clinical use of HIVIG, particularly since IgG3 is more vulnerable to proteolytic enzymes than other isotypes. Moreover they suggest that HIV-1 vaccines should induce high titer IgG3 responses.