Wimpy antibody isotypes protect against antibody-mediated disease

IgG是大多数哺乳动物中主要的循环IG类。小鼠和人都有4个IgG 同种型，其诱导效应机制的能力不同。鼠IgG 1激活补体较差， 最短的IgG铰链区（其可限制免疫复合物（IC）形成），并且仅结合1个刺激性抗体。 Fcγ受体（FcγR）。人IgG 4具有与小鼠IgG 1相似的特性， 因为它自发地形成单价的双特异性分子。这些观察提出了 为什么小鼠IgG 1和人IgG 4进化的问题，尽管他们可能降低损害的能力， 病原体我们假设这些同种型通过限制宿主损伤提供了选择性优势， 反应，并研究了这一点，通过比较抗体（Ab）介导的疾病的发展，在γ1-充足和 缺陷小鼠我们的研究结果支持我们的假设：γ1-充足的小鼠不受免疫的损害， 而同样免疫的γ1缺陷小鼠死于补体和Fcγ R非依赖性 肾小球毛细血管被大IC阻塞。IgG 1抗体抑制大IC形成，并且作用更大 比具有更长铰链区的IgG 2a或IgG 2b更有效。γ1缺陷小鼠也会产生2种补体- 和Fcγ R依赖性疾病，胶原诱导的关节炎和实验性自身免疫性重症肌无力， 比相同遗传背景的γ1-充足小鼠更频繁和更严重。 这些观察提出了三个重要问题：（1）铰链区是否存在差异 长度充分解释了IgG 1比其他IgG同种型更大的破坏大IC形成的能力;（2） 我们对小鼠IgG同种型的观察与人类相关;（3）小鼠IgG 1能否改善已建立的 Ab介导的疾病。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IgG抑制Ab-1的能力。 介导的疾病。我们将交换小鼠IgG 1和IgG 2b铰链区，最小化和最大化IgG 1铰链区， 区域长度和使用嵌合单克隆抗体产生的铰链区是否短的限制 补体依赖性疾病模型和补体非依赖性疾病模型中的疾病严重程度。 2.确定我们对小鼠IgG同种型的观察是否与人类相关。嵌合抗TNP 具有人γ1、γ2、γ3或γ4恒定区的mAb，以及具有突变的γ 1、γ 2、γ3或γ4恒定区的抗TNP mAb。 将产生防止单价双特异性Ab分子形成的人γ4恒定区， 比较体外破坏IC产生和体内预防IC肾病的能力。 3.确定在诱导效应子功能方面相对较差的Ab同种型是否可以抑制 建立Ab介导的疾病。研究将使用以下主动和被动小鼠模型进行： 获得性大疱性表皮病，一种由Abs引起的补体和Fcγ R依赖性水疱性皮肤病， VII型胶原（Col 7），以确定IgG 1抗Col 7抗体是否可导致已建立的疾病消退。

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.