Fine needle aspiration of human lymph nodes reveals cell populations and soluble interactors pivotal to immunological priming

Abstract

Lymph node (LN) fine needle aspiration (LN FNA) represents a powerful technique for minimally invasive sampling of human lymph nodes in vivo and has been used to good effect to directly study aspects of the human germinal center response. However, systematic deep phenotyping of the cellular populations and cell-free proteins recovered by LN FNA has not been performed. Thus, we studied human cervical LN FNAs as a proof-of-concept and used single-cell RNA-sequencing and proteomic analysis to benchmark this compartment, define the purity of LN FNA material, and facilitate future studies into this immunologically pivotal environment. Our data provide evidence that LN FNAs contain bone fide LN-resident innate immune populations, with minimal contamination of cells or proteins from blood. Examination of these populations reveals unique biology not predictable from equivalent blood-derived populations. LN FNA supernatants represent a specific source of lymph- and lymph node-derived proteins, and can, in combination with transcriptomic approaches, identify likely receptor-ligand interactions. This study provides the first description of the types and abundance of immune cell populations and cell-free proteins that can be efficiently studied by LN FNA. These findings are of broad utility for understanding LN physiology both in health and disease, including infectious or autoimmune perturbations, and in the case of cervical nodes, neuroscience.