Wimpy antibody isotypes protect against antibody-mediated disease

在大多数哺乳动物中，免疫球蛋白是主要的循环免疫球蛋白。小鼠和人都有4种免疫球蛋白 同种类型，在诱导效应器机制的能力上存在差异。小鼠IgG1激活补体能力差，有 最短的免疫球蛋白铰链区(可能限制免疫复合体(IC)的形成)，仅与1个刺激物结合 Fcγ受体(FcγR)。人免疫球蛋白G4具有与小鼠免疫球蛋白1相似的特征，其能力应该更弱 形成IC，因为它自发地形成单价、双特异性分子。这些观察结果提高了 为什么小鼠IgG1和人IgG4进化，尽管它们的损伤能力可能降低 病原体。我们假设这些亚型通过限制对寄主的破坏而提供选择性优势。 反应，并通过比较抗体(Ab)介导的疾病的发展情况在γ1充足和 有缺陷的小鼠。我们的结果支持我们的假设：γ1基因充足的小鼠不会因免疫而受到损害 有效抗原，而相同免疫的γ1缺陷小鼠死于补体和FcγR非依赖性 大ICs引起的肾小球毛细血管阻塞。IgG1抗体抑制大的IC形成并起更大的作用 比IgG2a或IgG2b更有效，后者的铰链区域更长。γ-1缺陷小鼠也会产生2-补体- 以及FcγR依赖型疾病、胶原性关节炎和实验性自身免疫性重症肌无力， 在相同的遗传背景下，比γ1充足的小鼠更频繁和更严重。 这些观察结果提出了三个重要的问题：(1)铰链区是否存在差异 长度充分解释了IgG1比其他免疫球蛋白同型更强的破坏大IC形成的能力；(2) 我们对小鼠免疫球蛋白同种类型的观察与人类相关；以及(3)小鼠免疫球蛋白1能否改善已建立的 AB介导性疾病。这些问题将通过以下具体目标加以解决： 1.确定短铰链区长度是否促进小鼠免疫球蛋白抑制抗体的能力 媒介疾病。我们将交换小鼠IgG1和IgG2b铰链区域，最小化和最大化IgG1铰链 区域长度和使用产生的嵌合单抗研究是否有短铰链区限制 补体非依赖型和补体依赖型疾病模型中的疾病严重性。 2.确定我们对小鼠免疫球蛋白同型的观察结果是否与人类相关。嵌合抗TNP 具有人γ1、γ2、γ3或γ4恒定区的单抗，以及具有突变的抗TNP单抗 将产生防止形成单价、双特异性抗体分子的人γ4恒定区，并 比较了体外干扰IC生产和体内预防IC肾脏疾病的能力。 3.确定在诱导效应器功能方面相对较差的抗体同型是否可以抑制 已建立的抗体介导性障碍。将使用主动和被动的小鼠模型进行研究 获得性大疱性表皮松解症，一种补体和FcγR依赖型水疱性皮肤病，由抗TO抗体引起 III型胶原蛋白(Col7)，以确定IgG1抗Col7抗体是否能导致既定疾病的消退。

IgG is the predominant circulating Ig class in most mammals. Both mouse and man have 4 IgG isotypes, which differ in ability to induce effector mechanisms. Murine IgG1 activates complement poorly, has the shortest IgG hinge region (which may limit immune complex (IC) formation) and binds to only 1 stimulatory Fcγ receptor (FcγR). Human IgG4 has similar characteristics to mouse IgG1 and should have even less ability to form ICs because it spontaneously forms univalent, bispecific molecules. These observations raise the question of why mouse IgG1 and human IgG4 evolved, despite their likely reduced ability to damage pathogens. We hypothesized that these isotypes provide a selective advantage by limiting host-damaging responses and studied this by comparing development of antibody (Ab)-mediated disorders in γ1-sufficient and deficient mice. Our results support our hypothesis: γ1-sufficient mice are not damaged by immunization with a potent antigen, while identically immunized γ1-deficient mice die from complement- and FcγR-independent obstruction of glomerular capillaries by large ICs. IgG1 Abs suppress large IC formation and do so more potently than IgG2a or IgG2b, which have longer hinge regions. γ1-deficient mice also develop 2 complement- and FcγR-dependent disorders, collagen induced arthritis and experimental autoimmune myasthenia gravis, more frequently and more severely than γ1-sufficient mice on the same genetic background. Three important questions are suggested by these observations: (1) do differences in hinge region length fully explain the greater ability of IgG1 than other IgG isotypes to disrupt formation of large ICs; (2) are our observations with mouse IgG isotypes human-relevant; and (3) can mouse IgG1 ameliorate an established Ab-mediated disease. These questions will be addressed by the following specific aims: 1. Determine whether short hinge region length promotes the ability of mouse IgG to suppress Ab- mediated disease. We will swap mouse IgG1 and IgG2b hinge regions and minimize and maximize IgG1 hinge region length and use the chimeric monoclonal Abs produced to study whether a short hinge region limits disease severity in complement-independent and complement-dependent disease models. 2. Determine whether our observations with mouse IgG isotypes are human-relevant. Chimeric anti-TNP mAbs that have human γ1, γ2, γ3 or γ4 constant regions, as well as an anti-TNP mAb that has a mutated human γ4 constant region that prevents formation of univalent, bispecific Ab molecules, will be produced and compared for ability to disrupt IC production in vitro and prevent IC kidney disease in vivo. 3. Determine whether an Ab isotype that is relatively poor at inducing effector functions can suppress an established Ab-mediated disorder. Studies will be performed with active and passive mouse models of epidermolysis bullosa acquisita, a complement- and FcγR-dependent blistering skin disease caused by Abs to collagen type VII (Col7), to determine whether IgG1 anti-Col7 Abs can cause established disease to regress.