Phenotypic and Functional Profiling of CD4 T Cell Compartment in Distinct Populations of Healthy Adults with Different Antigenic Exposure

BackgroundMultiparameter flow cytometry has revealed extensive phenotypic and functional heterogeneity of CD4 T cell responses in mice and humans, emphasizing the importance of assessing multiple aspects of the immune response in correlation with infection or vaccination outcome. The aim of this study was to establish and validate reliable and feasible flow cytometry assays, which will allow us to characterize CD4 T cell population in humans in field studies more fully. Methodology/Principal FindingsWe developed polychromatic flow cytometry antibody panels for immunophenotyping the major CD4 T cell subsets as well as broadly characterizing the functional profiles of the CD4 T cells in peripheral blood. We then validated these assays by conducting a pilot study comparing CD4 T cell responses in distinct populations of healthy adults living in either rural or urban Kenya. This study revealed that the expression profile of CD4 T cell activation and memory markers differed significantly between African and European donors but was similar amongst African individuals from either rural or urban areas. Adults from rural Kenya had, however, higher frequencies and greater polyfunctionality among cytokine producing CD4 T cells compared to both urban populations, particularly for “Th1” type of response. Finally, endemic exposure to malaria in rural Kenya may have influenced the expansion of few discrete CD4 T cell populations with specific functional signatures. Conclusion/SignificanceThese findings suggest that environmentally driven T cell activation does not drive the dysfunction of CD4 T cells but is rather associated with greater magnitude and quality of CD4 T cell response, indicating that the level or type of microbial exposure and antigenic experience may influence and shape the functionality of CD4 T cell compartment. Our data confirm that it is possible and mandatory to assess multiple functional attributes of CD4 T cell response in the context of infection.

研究背景
多参数流式细胞术（Multiparameter Flow Cytometry）已在小鼠与人类中揭示了CD4 T细胞（CD4 T cell）应答广泛的表型与功能异质性，凸显了结合感染或疫苗接种结局评估免疫应答多维度特征的重要性。本研究旨在建立并验证可靠且可行的流式细胞术检测体系，以便在实地研究中更全面地表征人类CD4 T细胞群体。

方法与主要结果
我们开发了多色流式细胞术（Polychromatic Flow Cytometry）抗体组合，用于外周血中主要CD4 T细胞亚群的免疫表型分型，并全面表征CD4 T细胞的功能特征。随后，我们通过一项预实验验证了该检测体系：对比居住在肯尼亚农村与城市地区的健康成年人不同群体的CD4 T细胞应答情况。本研究结果显示，非洲与欧洲供者的CD4 T细胞活化及记忆标志物表达谱存在显著差异，但来自肯尼亚农村与城市地区的非洲个体之间并无明显差异。然而，与城市人群相比，肯尼亚农村地区的成年人在产生细胞因子的CD4 T细胞中具有更高的细胞频率与更强的多功能性，尤其在1型辅助T细胞（"Th1"）应答中表现更为突出。最后，肯尼亚农村地区人群的地方性疟疾暴露可能影响了少数具有特定功能特征的CD4 T细胞亚群的扩增。

结论与意义
上述结果表明，环境诱导的T细胞活化并不会导致CD4 T细胞功能失调，反而与CD4 T细胞应答的更强强度与更佳质量相关，提示微生物暴露水平/类型以及抗原暴露经历可能会影响并塑造CD4 T细胞库的功能特征。本研究数据证实，在感染情境下评估CD4 T细胞应答的多维度功能特征不仅可行，且极具必要性。