Alternations in the Splenic Marginal Zone with Age

Splenic marginal zones are architecturally organized to generate a rapid response against blood- borne antigens entering the spleen. The marginal zone is a distinct anatomical micro-environment whose main components include the marginal zone macrophages, the marginal zone B cells, the marginal zone sinus, and the metallophilic macrophages. Marginal zone macrophages, in partnership with marginal zone B cells, are particularly important in host defense against T-independent pathogens and are crucial for the prevention of diseases such as Streptococcus pneumonia. It has been widely reported that with the advancement of age there is a higher rate of mortality as a result of bacterial pneumonia when compared to the young. My objective here was to determine if there are age related changes in the cellular components of the marginal zone in old versus young mice. Gross architectural changes in the marginal zones of old mice when compared to young mice were found and that disruptions were observed among the many components of the marginal zone, including: marginal zone macrophages, marginal zone B cells, the marginal zone sinus lining cells, and the metallophilic macrophages. The reduction in marginal zone macrophages in individual old mice also statistically correlated with reduced frequency of marginal zone B cells. These findings further strengthen a partnership of marginal zone macrophages and marginal zone B cells. Furthermore, the phagocytic properties of marginal zone macrophages were examined live on a per cell basis and no differences in phagocytosis of old marginal zone macrophages when compared to young were found, demonstrating that it is this reduction in the marginal zone macrophage population that contributes to the decline in the T-independent immune response reported with age. Results obtained from these studies can provide insight for the proper response needed to clear pathogens that have been shown to be detrimental in the old