目的：通过测定小儿外周血中B淋巴细胞CD21的表达，探讨新生儿体液免疫功能低下、免疫球蛋白合成不足的原因。方法：对不同年龄组小儿，利用流式细胞仪对外周血B淋巴细胞及CD21的表达进行检测；同时测定其血清免疫球蛋白水平。结果：新生儿组的外周血中表达CD21的B淋巴细胞比例和数目明显低；B淋巴细胞表达CD21位点的平均荧光强度（MFI）也明显降低，说明新生儿B淋巴细胞表达CD21的表达量低下。除了新生儿组IgG水平高于婴幼儿组外，血清免疫球蛋白水平也随着年龄的增长，呈逐渐升高的趋势。结论：新生儿乃至小婴幼儿体液免疫功能不足、免疫球蛋白水平低下的原因与B淋巴细胞功能及CD21的低表达有关。［中国当代儿科杂志，2007，9（6）：546-548］

OBJECTIVE: To study the cause of low immunologic function and insufficiency of immunoglubulin synthesis in neonates by detecting CD21 expression in B lymphocytes in different age group children.MethodsThis study consisted of three age group children: 2-26 days (n=18), 6 months-2 years (n=12) and 3-12 years (n=17). CD21 expression in B lymphocytes was detected with flow cytometry. Serum levels of immunoglobulins were measured by immunoturbidimetry. RESULTS: The percentage and the number of B lymphocytes expressing CD21 in the neonate group were significantly lower than in the other two age groups. The neonate group also showed lower mean fluorescence intension (MFI) of CD21. The percentage and the number of B lymphocytes expressing CD21 as well as the MFI of CD21 increased significantly with the age. The serum levels of IgA and IgM in the neonate group were noticeably lower than those in the other two age groups. The serum levels of IgA and IgM also increased significantly with the age. CONCLUSIONS: Low CD21 expression in B lymphocytes may be related to low function of humoral immunity in neonates.［Chin J Contemp Pediatr, 2007, 9 (6):546-548］