Changes in immune cell subtypes during ageing

The immune system comprises many different types of cells, each with different functions and properties during immune defence. The numbers and types of immune cells in the circulation is highly dynamic and regulated by infections, ageing and certain types of cancers. It is recognised that immune function decreases during ageing, but the biological age at which these functional changes occur is variable, and how ageing affects the different sub-types of lymphocytes, monocytes and NK cells in the circulation is not fully defined. In this study, we recruited 24 healthy volunteers over the age range of 23y to 89y and measured the numbers of different subclasses of circulating cells by immuno-phenotyping and flow cytometry. We show increased monocyte:lymphocyte ratios in a >50y cohort and most T cell subsets were decreased, except for CD4+ cells, which were increased in this cohort. In addition, there was NK cell expansion and increased HLA-DR+ T cells, but decreased numbers of classical monocytes and increased numbers of CD4+ monocytes in this >50y cohort. These data indicate that healthy ageing is associated with changes in both the major cell groups but also individual subclasses of cells, and these are likely to result from continuous immune challenge and impaired development.