Fisher, Jacob S

Abstract Aging dramatically impacts T cells, contributing to diminished and delayed responses to infection. While the development and maintenance of lymphocytes certainly undergo intrinsic changes with age, the contribution of cell-extrinsic forces, such as the aging tissue microenvironment, has been difficult to uncouple. Macroscopic changes to the lymph nodes have been well described, but the impact of aging on lymph node stromal subsets is less understood. Here, we visualized naïve T cell migration in the aged murine lymph node using live-cell 2-photon microscopy and determined that T cell motility was impaired in regions of increased fibrotic deposition. Using fluorescent reporters for Ccl19 and Cxcl12, homeostatic chemokines important for stromal:lymphocyte crosstalk, we also found that the distribution of stromal cells expressing these chemokines was altered with age, and that migrating naïve T cells were excluded from regions of chemokine expression. Flow cytometric analyses of fibroblastic reticular cells (FRCs) revealed decreased proportions of FRCs within the mesenteric lymph nodes and decreased putative FRC progenitors in the skin-draining lymph nodes. FRC progenitors at both sites had reduced surface expression of lymphotoxin-beta receptor, an important receptor for FRC differentiation and maintenance. We hypothesize that age-associated changes to FRC maturation contribute to increased lymph node fibrosis and altered localization of homeostatic factors. Current studies have indicated that in vitro cultured lymph node fibroblasts are sensitive to TNF-alpha and respond by increasing expression of alpha-smooth muscle actin, suggesting a mechanism by which aging remodels the lymph node microenvironment.

Abstract The aging immune system responds poorly to infection and vaccination, producing reduced numbers of germinal centers, low affinity antibody titers, and reduced B cell memory. Prolonged contacts between activated B cells and CD4+ T cells are crucial to germinal center formation and T follicular helper cell (Tfh) differentiation, but it is unclear how aging impacts the quality of this interaction. Peptide immunization confirmed that aged mice have less expansion of antigen-specific germinal center B cells and reduced antibody titers. Furthermore, aging was associated with decreased CD4+ T conventional cells and accumulated Tfh cells and regulatory T cells, even in naïve mice. Despite increased numbers, our results indicate that aged Tfh have decreased metabolic function, which may have repercussions on germinal center responses. To determine the contribution of cell-extrinsic influences on antigen-specific Tfh induction, we adoptively transferred young, antigen-specific B and CD4+ naïve T cells into aged hosts prior to peptide immunization, which resulted in reduced antigen-specific germinal center B cell and Tfh expansion and reduced antibody titers when compared to young hosts. The results from these experiments emphasize the importance of the lymphoid microenvironment in germinal center initiation and maintenance. We hypothesize that age-associated Tfh accumulation may impair antigen-specific Tfh induction and subsequent germinal center responses. Current studies use live-cell 2-photon microscopy to track the impact of age on lymphocyte motility and Tfh:B interactions, in order to determine the relative contributions of aged APCs, non-specific aged Tfh, and aged regulatory T cells to germinal center deficiency. Research supported by the Mayo Clinic Robert and Arlene Kogod Center on Aging Innovation Award UL1R002377