The expanded null cell compartment in ageing: increase in the number of natural killer cells and changes in T-cell and NK-cell subsets in human blood.

Analysis of the subpopulations of mononuclear cells in human blood in ageing has revealed a striking increase in the number of null cells, defined as non-T, non-B, non-monocyte cells, and a decrease in the number of T and B cells. By using recently developed monoclonal antibodies against natural killer cells in combination with T-cell markers in two-wavelength immunofluorescence, we were able to define 13 subpopulations of mononuclear cells and compare them in two groups of persons, respectively aged 25-34 and 75-84 years, all fulfilling the stringent admission criteria for immunogerontological studies described in the SENIEUR protocol, and thus all to be considered as optimally healthy and immunologically uncompromised. We found that the increased null cell population in the aged is a result of an increase in the numbers of NK cells, mostly the CD16+Leu7+ subset. The number of CD8+ suppressor/cytotoxic cells is decreased. This is due to a decrease of the number of CD8+Leu7- cells. All NK and T-cell subsets bearing the Leu7 antigen, namely CD16+ Leu7+, CD4+Leu7+ and CD8+Leu7+, are increased. These changes can be due to defects of the ageing immune system, but they can also represent the optimal state of the immune system in the healthy aged and may be linked to survival. These values can be used as reference values for the 75-84 years age group and serve to monitor attempts to reconstitute the immune defects in ageing.