Person:

Fletcher, Anne Louise

Within lymph nodes, non-hematopoietic stromal cells organize and interact with leukocytes in an immunologically important manner. In addition to organizing T and B cell segregation and expressing lymphocyte survival factors, several recent studies have shown that lymph node stromal cells shape the naïve T cell repertoire, expressing self-antigens which delete self-reactive T cells in a unique and non-redundant fashion. A fundamental role in peripheral tolerance, in addition to an otherwise extensive functional portfolio, necessitates closer study of lymph node stromal cell subsets using modern immunological techniques; however this has not routinely been possible in the field, due to difficulties reproducibly isolating these rare subsets. Techniques were therefore developed for successful ex vivo and in vitro manipulation and characterization of lymph node stroma. Here we discuss and validate these techniques in mice and humans, and apply them to address several unanswered questions regarding lymph node composition. We explored the steady-state stromal composition of lymph nodes isolated from mice and humans, and found that marginal reticular cells and lymphatic endothelial cells required lymphocytes for their normal maturation in mice. We also report alterations in the proportion and number of fibroblastic reticular cells (FRCs) between skin-draining and mesenteric lymph nodes. Similarly, transcriptional profiling of FRCs revealed changes in cytokine production from these sites. Together, these methods permit highly reproducible stromal cell isolation, sorting, and culture.

Lymph node stromal cells (LNSCs) closely regulate immunity and self-tolerance, yet key aspects of their biology remain poorly illuminated. Comparative transcriptomic analyses of murine LNSC subsets revealed expression of important immune mediators, growth factors, and novel structural components. Pairwise analyses of ligands and cognate receptors across hematopoietic and stromal subsets suggested a complex web of cross-talk. Compared with skin and thymic fibroblasts, fibroblastic reticular cells (FRCs) were enriched in genes relevant to cytokine signaling. LNSCs from inflamed lymph nodes upregulated acute phase response genes, chemokines, and antigen presentation genes. Poorly studied podoplanin−CD31− LNSCs showed similarities to FRCs, but lacked IL-7 expression, and were identified as myofibroblastic integrin α7+ pericytes. Together these data comprehensively describe the transcriptional characteristics of LNSC subsets.