Lymph node immune landscaping in COVID-19.

The regulation of follicular (F) and germinal center (GC) immune reactivity in human lymph nodes (LNs), particularly during the acute stages of viral infections, remains poorly understood. We have analyzed lung-draining lymph nodes (LD-LNs) from COVID-19 autopsies using multiplex imaging and spatial transcriptomics to examine the immune landscape and with respect to the aging. We identified three subgroups of Reactive Follicles (RFs) based on Bcl6 prevalence, RF-Bcl6no/low, RF-Bcl6int and RF-Bcl6high. RF-Bcl6high tissues express a distinct B/Tfh immune landscape associated with increased prevalence of proliferating B- and Tfh-cell subsets. Comparison between LD-LNs and matched subdiaphragmatic LNs revealed a disconnected Bcl6 reactivity between the two anatomical sites. LD-LNs Bcl6 reactivity was associated with a distinct spatial transcriptomic profile. TH1-associated genes/pathways (e.g. CXCR3, STAT5, TNF signaling) were significantly upregulated in RF-Bcl6no/low tissues while the RF-Bcl6high tissues exhibited significant upregulation of GC-promoting genes/pathways (e.g. CXCL13, B cell receptor signaling). Despite the similar prevalence, the in-situ transcriptome profiling indicates a higher monocyte/macrophage functionality in “Aged” compared to “Young” follicles from donors with comparable Bcl6 reactivity. Our findings reveal a heterogeneous F/GC landscape in COVID-19 LD-LNs and highlight specific molecular targets and pathways that could regulate human F/GC immune dynamics during acute viral infections.

人类淋巴结（human lymph nodes, LNs）中滤泡（follicular, F）与生发中心（germinal center, GC）的免疫反应调控机制，尤其是在病毒感染急性期，目前仍不甚明晰。本研究利用多重成像（multiplex imaging）与空间转录组学（spatial transcriptomics）技术，对新冠病毒感染尸体解剖样本的肺引流淋巴结（lung-draining lymph nodes, LD-LNs）展开分析，以探究其免疫景观并结合衰老状态开展研究。研究人员基于B细胞淋巴瘤6因子（Bcl6）的表达水平，鉴定出三类反应性滤泡（Reactive Follicles, RFs）亚群：RF-Bcl6阴性/低表达（RF-Bcl6no/low）、RF-Bcl6中等表达（RF-Bcl6int）与RF-Bcl6高表达（RF-Bcl6high），其中RF-Bcl6高表达组织呈现独特的B细胞/滤泡辅助性T细胞（B/Tfh）免疫景观，伴随增殖性B细胞与滤泡辅助性T细胞亚群比例升高。通过对比肺引流淋巴结与配对膈下淋巴结，研究发现二者的Bcl6免疫反应性存在显著脱节，且肺引流淋巴结的Bcl6反应性对应独特的空间转录组特征。在RF-Bcl6阴性/低表达组织中，1型辅助性T细胞（Th1）相关基因/通路（如CXCR3、STAT5、肿瘤坏死因子（TNF）信号通路）显著上调；而RF-Bcl6高表达组织则显著上调生发中心促进相关基因/通路（如CXCL13、B细胞受体（B cell receptor）信号通路）。尽管Bcl6反应性水平相近，但原位转录组分析（in-situ transcriptome profiling）显示，在Bcl6反应性相当的供体中，老年组滤泡的单核细胞/巨噬细胞（monocyte/macrophage）功能显著高于青年组滤泡。本研究揭示了新冠患者肺引流淋巴结中滤泡/生发中心免疫景观的异质性，并明确了可调控急性病毒感染期间人类滤泡/生发中心免疫动态的特定分子靶点与通路。