Evidence for Renewal and Reconstitution of Marginal Zone Macrophages in Young and Aged Mice

Aging in humans and mice correlates with decline in immune health, affecting both innate and adaptive immunity. Response against blood-borne bacterial pathogens is compromised because of the deterioration of the marginal zones of the spleen and decrease in frequency of marginal zone macrophages (MZM). This thesis asked if low cell turnover is the cause for the decrease of MZM, using cell proliferation to indicate cell turnover in spleens of mice. First, evidence showed MZM proliferation occurred in spleens of young mice and was decreased in the MZM from aged mice. Second, transfer of young bone marrow into old mice replenished some of the lost MZM. The experimental design used histological sections and flow cytometry to detect MZM that had proliferated. These results may explain the reason for deteriorated marginal zones, as well as a potential therapeutic to reestablish MZM and promote protective immune response to bacteria in the aged