Immunoglobulin subclasses and IGIV

摘要：为了确定免疫球蛋白亚类在中和HIV-1的能力上是否存在差异，将多克隆HIVIG通过蛋白A柱，收集并显示适当的组份是&gt；89%纯的IgG1、IgG2和IgG3(IgG4没有足够的数量用于研究)。所有三个亚类都显示与所有主要的HIV-1蛋白(IgG1和GT；IgG2和GT；IgG3)结合。相反，通过合胞体抑制和无细胞病毒中和检测，IgG3在中和HIV-1的能力方面比其他亚类更有活性(IgG3和GT；IgG1和GT；IgG2)。HIVIG及其亚类的中和能力也取决于病毒株，因此嗜T细胞(R4)病毒比嗜巨噬细胞(R5)病毒更敏感。IgG3不同于IgG1和IgG2，因为它的铰链区更长、更灵活。为了测试这对中和病毒是否重要，用木瓜酶将免疫球蛋白组分消化成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。与来自其他免疫球蛋白亚类的F(Ab)2片段相比，来自IgG3的F(Ab)2片段保留了其更好的中和HIV-1的能力，这表明IgG3的较长铰链区使IgG3能够更有效地中和HIV-1。这些发现对HIVIG的制造和临床应用具有指导意义，特别是因为IgG3比其他同种类型更容易受到蛋白水解酶的影响。此外，他们还建议，HIV-1疫苗应能诱导高滴度的IgG3反应。

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.