No abstract

SummaryLymph nodes (LN) are secondary lymphoid organs spread throughout the lymphatic system. They function to filter pathogenic material from the lymphatic fluid to maintain the health of the organism. Subcapsular sinus macrophages (SCSM) are among the first‐responders within the LN due to their strategic location within the subcapsular sinus region. These macrophages aid the delivery of immune complexes to B cells and follicular dendritic cells (FDC) within the LN. Here we show an increase in SCSM and other macrophage populations within aged LN. However, immune complex uptake by macrophages within LN was not altered with age, nor was immune complex uptake by B cells. LN stromal cell populations, important in immune responses and the localization and survival of leucocytes, were altered in their representation and distribution in aged LN. In particular, FDC regions were decreased in size and had decreased chemokine CXCL13 expression. Furthermore, the retention of immune complexes by FDC was decreased in aged LN at 24 hr post‐injection. As FDC are important in the maintenance of germinal centre responses, the decreased retention of immune complex in aged LN may contribute to the reduced germinal centre responses observed in aged mice.

SummaryMarginal zone (MZ) B cells are positioned within the spleen to capture blood‐borne antigen and immune complexes and deliver them to follicular dendritic cells in the B‐cell follicles. We show that within the spleens of aged mice antigen capture by MZ B cells, and their ability to shuttle between the follicle and MZ, were impaired. The ability of aged MZ B cells to migrate towards the MZ chemoattractant sphingosine‐1‐phosphate was increased, suggesting that aged MZ B cells had a greater propensity to be retained within the MZ. An extrinsic impairment in aged B‐cell migration towards the MZ was demonstrated using bone marrow chimeras. The follicular shuttling of MZ B cells derived from either young or aged bone marrow was similarly reduced in aged recipient spleens, showing that ageing effects on splenic stromal cells were responsible for the impaired follicular shuttling of MZ B cells. MZ B cells rapidly mount T‐cell‐independent (TI) antibody‐responses to microbial polysaccharide antigen. In aged mice the ability to produce immunoglobulins in response to the TI type 1 antigen TNP‐LPS was impaired. These ageing‐related changes to the MZ and MZ B cells have implications for the clearance of blood‐borne pathogens. Indeed elderly people have increased susceptibility to Streptococcus pneumoniae, a TI antigen, and decreased responses to vaccination. A thorough analysis of the mechanisms that underpin the ageing‐related decline in the status of the MZ and MZ B cells will help the design of novel treatments to improve immunity in the elderly.