Supplementary Material for: Cytomegalovirus Infection Minimally Affects the Frequencies of B-Cell Phenotypes in Peripheral Blood of Younger and Older Adults

<b><i>Background:</i></b> An accumulation of late-differentiated CD8+ T-cells together with fewer B-cells and seropositivity for cytomegalovirus (CMV) characterises an ‘immune risk profile' associated with mortality in elderly people and represents one of the hallmarks of ‘immunosenescence'. <b><i>Objectives:</i></b> While differences in memory T-cell phenotypes between young and old people have been intensively studied, and the role of CMV is well-accepted as a driving force in this regard, the impact of CMV on B-cells, if any, has been relatively neglected thus far. <b><i>Methods:</i></b> Here, we avail ourselves of blood samples from participants of the Berlin Aging Study II (BASE-II) to compare peripheral blood B-cell differentiation phenotypes of 140 age- and gender-matched CMV-seronegative or -seropositive adults aged between 24 and 85 years using multicolour flow cytometry analysis. <b><i>Results:</i></b> We found that the frequencies of naïve B-cells within the CD19+ population were not significantly different in younger and older CMV-seronegative people. This was also true in CMV-seropositive subjects. The frequencies of late-differentiated B-cells were also not different in CMV-negative elderly and young. However, in marked contrast to the T-cell compartment, this was also true for late differentiated B-cells. Within age groups, the most marked differences in the distribution of B-cell phenotypes were between CMV-seronegative and -seropositive subjects, for both genders. <b><i>Conclusion:</i></b> These results emphasize the importance of including CMV serostatus in the analysis of immune signatures. Because the proportion of the population infected with CMV increases with age, the effect of CMV rather than age could confound analyses seeking age-associated changes to human immunity.

**背景**：终末分化CD8+ T细胞蓄积、B细胞数量减少以及巨细胞病毒（Cytomegalovirus, CMV）血清阳性，共同构成了与老年人死亡率相关的「免疫风险表型」，同时也是「免疫衰老（immunosenescence）」的标志性特征之一。
**目的**：尽管青年与老年群体间的记忆T细胞表型差异已得到广泛研究，且巨细胞病毒（CMV）在其中的驱动作用已被学界广泛认可，但迄今为止，CMV对B细胞的影响（若存在的话）却相对被忽视了。
**方法**：本研究借助柏林衰老研究二期（Berlin Aging Study II, BASE-II）参与者的血液样本，采用多色流式细胞术（multicolour flow cytometry）分析，对比了140名年龄介于24至85岁、年龄与性别匹配的巨细胞病毒血清阴性或阳性成年人的外周血B细胞分化表型。
**结果**：本研究发现，在CMV血清阴性的青年与老年个体中，CD19阳性细胞群内初始B细胞（naïve B-cells）的占比无显著差异；CMV血清阳性受试者中亦是如此。CMV阴性的青年与老年群体的终末分化B细胞（late-differentiated B-cells）占比同样无明显差异。但与T细胞组分形成鲜明对比的是，终末分化B细胞的占比也符合这一规律。在各年龄组内，无论男女，B细胞表型分布最显著的差异均存在于CMV血清阴性与阳性受试者之间。
**结论**：上述结果凸显了在免疫特征谱（immune signatures）分析中纳入巨细胞病毒血清状态的重要性。由于人群中巨细胞病毒感染率随年龄增长而升高，因此在探究人类免疫的年龄相关变化时，巨细胞病毒的影响可能会干扰分析结果，而非年龄本身。