During human ageing, which immune cell sub-types are most affected?
From my Immunology notes:

*Decrease in hematopoietic stem cells resulting in a reduction of Affector cells. Erythroid and myeloid progeny cells don't seem to be affected.

*Fewer pro-B cells, resulting in fewer affector B-cells.

*Lymphoid progenitors in the bone marrow and thymus mature.

*Lymphocytes in secondary lymphoid organs.

For the Innate system:

*Neutrophils have a reduced capacity for Oxidative bursts, Batericidal activity, and Chemotaxis.

*Macrophages have a reduced capacity for phagocytic activity, oxidative bursts, and MHC II expression (which impairs their ability to present antigen and initiate CD4 Helper T-Cell responses).

*NK Cells have a reduced capacity for Cytotoxicity, proinflammatory cytokines and chemokines,and proliferation in response to IL-2. However, the total number of NK cells increases.

The sources: Both clinical (it was at a teaching hospital) and Aging and Immune System, Chapter 33 of the class text: Cellular and Molecular Immunology