The relatively low concentration of serum Hsp70 levels in our study compared to Rea et al., who found that individuals aged 90 and older have serum Hsp70 levels of about 20 ng/mL (Rea et al., 2001), does not contradict either study. A recentPopulation. Contrary to our hypothesis, we did not demonstrate any genetic associations that explain the differences in serum Hsp70. This could be a true finding or the consequence of the relatively small sample size of our populations. More likely, it is possible that the differences in serum Hsp70 levels that we demonstrated are a downstream effect of genetic differences elsewhere in the metabolic pathway. Future genetic studies of Hsp70 levels could focus on such genes.

4.3. Conclusions
Our study of serum Hsp70 levels in centenarian offspring compared to controls (Terry et al., 2004) and those of Rea et al. (2001) and Jin et al. (2004) showed that serum Hsp70 levels are lower in individuals who reach an advanced age. In addition, it suggests that low serum Hsp70 levels are associated with longevity independent of other covariates such as age, gender, race, income, alcohol, cardiovascular disease, and a variety of other age-related diseases. No statistically significant associations were found with two tagSNPs within Hsp70 genes. Further investigation is needed to determine why centenarians and centenarian offspring have low levels of serum Hsp70 and to better understand the role of genetic polymorphisms in this observation.

Heat shock protein 
J. Immunol., Binder, R.J., Harris, M.L., Menoret, A., Srivastava, P.K., Saturation, competition, and specificity in the interaction of heat shock proteins (Hsp) gp, Hsp and Hsp with CD b+ cells. J. Immunol., Clayton, A., Turkes, A., Navabi, H., Mason, M.D., Tabi, Z., Induction of heat shock proteins in B-cell exosomes. J. Cell Sci., Calderwood, S.K., Theriault, J.R., Gong, J., Message in a bottle: the role of the Hsp70 family in anti-tumor immunity. Eur. J. Immunol., Effros, R.B., Zhu, X., Walford, R.L., Stress response of senescent T lymphocytes: reduced Hsp is independent of the proliferative block. J. Gerontol. B B Gastpar, R., Gehrmann, M., Bausero, M.A., Asea, A., Gross, C., Schroeder, J.A., Multhoff, G., Heat shock protein surface-positive tumor exosomes stimulate migratory and cytolytic activity of natural killer cells. Cancer Res., Georgopoulos, C., Welch, W.J., Role of the major heat shock proteins as molecular chaperones. Annu. Rev. Cell Biol., Hartl, F.U., Molecular chaperones in cellular protein folding. Nature, Hsu, A.L., Murphy, C.T., Kenyon, C., Regulation of aging and age-related disease by DAF- and heat-shock factor. Science, Hunter-Lavin, C., Davies, E.L., Bacelar, M.M., Marshall, M.J., Andrew, S.M., Williams, J.H., Hsp release from peripheral blood mononuclear cells. Biochem. Biophys. Res. Commun., Jin, X., Wang, R., Xiao, C., Cheng, L., Wang, F., Yang, L., Feng, T., Chen, M., Chen S., Fu X., Deng J., Wang R., Tang F., Wei Q., Tanguay R.M. Wu T. Serum and lymphocyte levels of heat shock protein in aging: a study in the normal Chinese population. Cell Stress Chaperones,

Acknowledgements
The authors thank Susana Fiorentino for helpful discussions and Edwina Asea and Diana T. Page for expert technical assistance. This work was supported in part by the National Institute on Aging grant K08AG22785 (to DFT); Paul Beeson Physician Faculty Scholar in Aging Awards (to DFT, TP, NB), the Ellison Medical Foundation Senior Scholar Award and RO1 AG-18728-01A1 (to NB); the National Institutes of Health grant RO1CA91889, institutional support from Scott & White Memorial Hospital and Clinic, Texas A&M University System Health Science Center College of Medicine, the Central Texas Veterans Health Administration and an Endowment from the Cain Foundation (to AA).

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