Assessment of lymph node stromal cells as an underlying factor in age related immune impairment to influenza infection

It is well established that aging negatively impacts immunity, resulting in inefficient responses to vaccinations and infections, like influenza. Fibroblastic reticular cells (FRCs) are the major stromal cell subset in lymph nodes and play an intricate role in the orchestration and control of adaptive immune responses. Although stromal cells have a major impact on immune responses, the impact of aging on LN stromal cells has yet to be determined. We sought to determine how aging impacts FRC number, phenotype and morphology at steady state and after influenza infection. An enzymatic and mechanical digestion was used to make single cell suspensions of lymph node stromal cells for analysis. Flow cytometry was performed to quantify the number and frequency of stromal cells in lymph nodes from young (13 weeks) and aged (19 months) C57BL/6 mice. To analyze stromal cell morphology, lymph nodes from young and aged mice were cryopreserved, and then sectioned for confocal microscopy. Quantitative analysis of lymph node stromal cells by flow cytometry revealed that there are no significant differences in the number stromal cells in young and aged lymph nodes at steady state, but after influenza infection aged FRCs fail to expand in number. Reduced proliferation and activation of aged FRCs, but not increased death leads to the decreased expansion. Microscopic analysis revealed that young and aged LN T cell zone FRCs have similar morphology at steady state and after infection. These results are the first evidence that aging alters lymph node stromal cells ability to respond to challenge. These changes in aged FRCs may be an underlying cause behind the impaired immune response to influenza infection found in the elderly.