- 期刊
IgG Subclasses and Their Deficiencies
免疫球蛋白亞羣及其缺乏症
摘要
免疫球蛋白G(Immunogloblin G)在人體免疫系統中，占極要的地位，依構造上的不同可分成4個亞群(subclass)，爲IgG1,IgG2,IgG3,IgG4其功能亦有差異。如IgG2與抗細菌外膜多醣體抗體的形成有關，IgG4則在過敏免疫反應上扮演一個角色。胎兒在母體內時，IgG1-4皆可自胎盤傳入，出生後各亞群濃逐漸降低，俟個體自行合成在2-10歲達到成人濃度。IgG全量可能正常而卻可能有某一亞群的缺乏，甚至有某一亞群量正常但無法産該亞群之某些特異性抗體(specific antibody)。而這些亞群的缺乏，有時常呈配對的出現，此可能與基因的排列有關。當懷疑有免疫球蛋白G亞群缺乏症時，除了必須注意各年齡層的正常範圍外，並要注意所使用的檢驗方法的敏感度。免疫球蛋白G亞群缺乏症的病人，可能完全沒有症狀，或可能有反覆性的感染及自體免疫疾病，治療是以免疫球蛋白定期注射治療。
關鍵字
無資料並列摘要
Immunoglobulin G is very important in the human humoral immune system. It consists of four subclasses: IgG1, IgG2, IgG3, and IgG4. These subclasses of IgG have different chemical and biological characteristics. IgG2 has been prominent in antibody responses to bacterial polysaccharide antigens. IgG4 is thought by some investigators to be related to allergic reactions. All IgG subclasses can be transported to the fetus via the placenta but at somewhat different rates, as will be discussed later. This passive antibody is progressively lost after birth, and soon after birth, synthesis begins in the infant. Adult levels of IgG subclasses are finally reached between 2-10 years of age in the following sequence: IgG3, then IgG1, followed by IgG4, and finally IgG2. IgG subclass deficiency may exist even though the total amount of immunoglobulin may be normal. Such a deficiency will not be recognized unless subclass assays are carried out. Defects in specific antibody formation also may exist when total levels of immunoglobulin classes and subclasses are normal. IgG subclass deficiency often involves more than one isotype. Combined deficiencies tend to relate to the isotype positions of the heavy chain genes on chromosome 14. The age-related normal range of values for each immunoglobulin class and subclass must be considered in evaluating the levels of IgG subclasses. Patients with IgG subclass deficiencies may have no symptoms, mild symptoms or severe recurrent or chronic infections. There also is an increased autoimmune disease frequency in IgG subclass deficiency patients.