A 6-month old boy is noted at his well-child visit to have very poor growth and weight gain since his last visit. His mother states that he was hospitalized for pneumococcal pneumonia, and has had several bad colds with purulent nasal discharge since he was born. His physician suspects an immunodeficiency, and laboratory results indeed reveal deficiency of a complement protein. Which of the following antibodies functions in the same manner as the missing complement protein in this child?
一名6个月大的男孩在健康儿童就诊时发现，自上次就诊以来，他的生长和体重增加非常差。他的母亲说，他因肺炎球菌肺炎住院，自出生以来多次患重感冒，鼻腔流脓涕。他的医生怀疑他有免疫缺陷，实验室结果也确实显示了补体蛋白的缺乏。下列哪一种抗体的功能与该患儿缺失的补体蛋白相同?
(A) IgA
(B) IgD
(C) IgE
(D) IgG
(E) IgM
答案解析：
该患者已经有过几种细菌感染，最明显的是肺炎链球菌感染。补体是天然免疫系统的一部分，是一组血清蛋白，与抗体活性一起工作，以清除病原体。具体来说，蛋白质C3b负责细菌的调理作用，很可能是这个孩子免疫系统中缺失的蛋白质。调理素能粘附微生物，促进白细胞趋化、抗原结合和吞噬，激活巨噬细胞和中性粒细胞杀伤机制。抗体IgG也是一种调理素，C3b和IgG是两种主要的调理素，负责抵御细菌。
正确答案：D
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