NK Cell Activity and T-Lymphocyte Proliferation in Healthy Centenarians" P. SANSONI, V. BRIANTI, F. FAGNONI, G. SNELLI, A. MARCATO, G . PASSERI, D. MONTI, A. COSSARIZZA, A N D C. FRANCESCHI Institute of General Clinical Medicine University of Parma Parma, Italy Institute of General Pathology University of Modena Modena, Italy Centenarians represent an extremely rare group of individuals (1:30,000) who likely reach this very advanced age because of well-preserved homeostatic and defense mechanisms. Because a well-preserved immune system should protect against pathogenic agents and transformed cells, we studied some parameters of the immune system of centenarians compared to those in young and middle-aged controls. The study population consisted of 23 centenarians (100-106 years old) in good general condition without acute illness affecting the immune functions. The control population consisted of 18 middle-aged subjects (50-68 years old) and 19 young ones (19-36 years old). Peripheral blood lymphomonocytes (PBL) were obtained by Ficoll-Paque density centrifugation from venous blood collected from a centenarian, a middle-aged person, and a young control subject the same day. Samples of 1 x los PBL, resuspended in RPMI 1640 with 10% A B serum, 2 m M / L ~-glutamine,100 p,g/ml streptomycin, and 100 U/ml penicillin, were stimulated with phytohemagglutinin (PHA, 1 p,g/ml), concanavalin A (Con A, 20 p,g/ml), or purified anti-CD3 monoclonal antibody (1:2,000, final concentration). Uptake of (")-thymidine was measured after 72 hours in culture, and the results were expressed as the mean counts per minute +- standard error of the mean (cpm -+ SEM). NK activity was measured in a 6-hour W r release cytotoxicity assay using the K 562 human erythroleukemia cell line as a target.' FIGURE 1 shows that the non-MHC restricted cytotoxic activity of PBL from centenarians is not significantly reduced from that in young controls. However, NK activity in the centenarian group was significantly (J < 0.006) higher than that in the middle aged group and in some instances was even higher than that in young controls. T-lymphocyte responses to PHA showed a progressive decline with age, and a highly significant reduction was observed in centenarians compared to young controls (FIG. 2). On the contrary, the lymphocyte proliferation induced by Con A or anti-CD3 was not significantly modified in either the middle-aged o r the centenarian group when compared with the young controls (FIG.2). It is generally reported that the immune function decreases with age, and a reduction in the absolute number and in the function of peripheral lymphocytes is aThis work was supported by a grant from Consiglio Nacionale delle Ricerche INV 9 2 . 3 . 146.

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FIGURE 1. NK cell activity of lymphomonocytes from centenarian, middleaged, and young control subjects against K-562 tumor cell targets. Mean responses of young (0),middle-aged subjects (A), and centenarians ( 0 ) .The comparison between centenarians and young control subjects showed no statistical differences. NK cell activity of the centenarians was statistically higher ( * = p < 0.006) than that in the middle-aged group. Statistical analysis by the Student t test was performed. The standard error was always < 3%.

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described.2 Our results show that not all T-cell responses in the healthy centenarians are reduced, and some important signal transduction pathways are intact. Although a progressive increase in cells with NK markers has been reported in the elderly,3 contradictory results of NK cell activity are described.kh Our results clearly show that the NK cell activity of the centenarians is not significantly reduced compared to that in young control subjects at all effector-to-target ratios. This increased cytolytic activity could be referred to as an expansion of a subset of NK cells with higher NK cell activity or to an increase in adhesion molecules on the surface of NK cells. On the whole, our results show that in the centenarians important immune functions such as T-lymphocyte proliferation and NK cell activity are well preserved and may contribute to reaching this far-advanced age.

FIGURE 2. Mitogen-dependent proliferative responses of lymphomonocytes from and centenarian (m), middle-aged young control subjects (0).The proliferative responses to PHA (1 kg/ml) showed a decline in middle-aged vs young subjects ( * = p < 0.05) and a further reduction in the centenarians vs young subjects ( * * = p < 0.005). Statistical analysis by the Student t test was performed.

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