Figure 1.

Age-associated changes in immune cell frequency and function. A mixture of mouse and human experiments show differences in both the frequency and function of cells in the innate and adaptive immune compartments. HSCs in the elderly are skewed toward differentiation into myeloid progenitors at the expense of lymphoid progenitors. Elderly individuals have fewer circulating monocytes and DCs, fewer tissue-associated DCs, normal tissue macrophages, and increased splenic DCs. Naïve T and B cells populations are diminished, though mature-like T and B cells are expanded. As a result, overall antibody production and specificity is diminished in the elderly. Despite increased numbers of splenic DCs, antigen presentation is lacking at these sites in the elderly. Pro-inflammatory cytokine levels are increased in the elderly, as seen in IL-6 and TNF levels in serum samples.