球蛋白免疫血清

唯一可以通过胎盘的免疫球蛋白——IgG ：你知道与不知道的

唯一可以通过胎盘的免疫球蛋白是什么？IgG（免疫球蛋白G的缩写）！IgG的功能作用主要在机体免疫中起保护作用，大多数抗菌、抗病毒；应对麻疹、甲型肝炎等，能有效地预防相应的感染性疾病。...

IgG是免疫球蛋白G(Immunoglobulin G，IgG)的缩写，是血清主要的抗体成分，约占血清Ig的75%。其中40～50%分布于血清中，其余分布在组织中。IgG是唯一可以通过胎盘的免疫球蛋白。IgG的功能作用主要在机体免疫中起保护作用，大多数抗菌、抗病毒；应对麻疹、甲型肝炎等，能有效地预防相应的感染性疾病。其指标对于诊断某些疾病具有意义。

Immunoglobulin G (IgG) is a type of antibody. It is a protein complex composed of four peptide chains—two identical heavy chains and two identical light chains arranged in a Y-shape typical of antibodymonomers. Each IgG has two antigen binding sites. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in the circulation.[1] IgG molecules are created and released by plasma B cells.

基本概述

IgG是免疫球蛋白G(Immunoglobulin G，IgG)的缩写。根据结构的不同将免疫球蛋白分为五种，IgG是人的免疫球蛋白之一，其他还有lgA、lgM、IgD和lgE.。

IgG是血清主要的抗体成分，约占血清Ig的75%。其中40～50%分布于血清中，其余分布在组织

IgG结构图

中。根据IgG分子中的r链抗原性差异，人IgG有四个亚型：IgG1、IgG2、IgG3、IgG4。

IgG主要由脾、淋巴结中的浆细胞合成和分泌，以单体形式存在。在个体发育过程中机体合成IgG的年龄要晚于IgM，在出生后的第三个月开始合成，3~5岁接近成年人的水平。40岁后逐渐下降。

Antibodies are major components of humoral immunity. IgG is the main type of antibody found in blood and extracellular fluid allowing it to control infection of body tissues. By binding many kinds of pathogens such as viruses, bacteria, and fungi, IgG protects the body from infection. It does this through several mechanisms: IgG-mediated binding of pathogens causes their immobilization and binding together via agglutination; IgG coating of pathogen surfaces (known as opsonization) allows their recognition and ingestion by phagocytic immune cells; IgG activates the classical pathway of the complement system, a cascade of immune protein production that results in pathogen elimination; IgG also binds and neutralizes toxins. IgG also plays an important role in antibody-dependent cell-mediated cytotoxicity (ADCC) and intracellular antibody-mediated proteolysis, in which it binds to TRIM21 (the receptor with greatest affinity to IgG in humans) in order to direct marked virions to the proteasome in the cytosol.[2] IgG is also associated with type II and type IIIhypersensitivity reactions.

IgG antibodies are generated following class switching and maturation of the antibody response and thus participate predominantly in the secondary immune response.[3] IgG is secreted as a monomer that is small in size allowing it to easily perfuse tissues. It is the only isotype that has receptors to facilitate passage through the human placenta, thereby providing protection to the fetus in utero. Along with IgA secreted in the breast milk, residual IgG absorbed through the placenta provides the neonate with humoral immunity before its own immune system develops. Colostrum contains a high percentage of IgG, especially bovine colostrum. In individuals with prior immunity to a pathogen, IgG appears about 24–48 hours after antigenic stimulation.

生理作用

IgG的功能作用主要在机体免疫中起保护作用，大多数抗菌、抗病毒；应对麻疹、甲型肝炎等，能有效地预防相应的感染性疾病。

IgG是唯一可以通过胎盘的免疫球蛋白。来自母体的IgG在出生后数月对防御白喉、麻疹、脊髓灰质炎等感染起着重要作用，母体传递给胎儿的IgG于生后6个月几乎全部消失，而婴儿自身产生IgG从3个月时才逐渐增多，故6个月后易患感染。3-5岁是渐接近成人水平。