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Blood lymphocyte subsets, serum immunoglobulins (Ig), response of lymphocytes to mitogens, and natural killer (NK) cell activity were evaluated as potential biomarkers for primate aging. All were evaluated in a cross-sectional study of 60 pigtailed macaques (Macaca nemestrina) ranging from 2 to 32 years of age. Lymphocyte responses to mitogens were lower in older animals than in most younger ones. NK cell activity showed no clear relation to age cohort. In a longitudinal study of lymphocyte subsets and immunoglobulins, class I restricted T cells (CD8+bri) of the memory (CD18+bri) subtype increased with age, whereas those of the naive (CD18+dull) subtype decreased with age in females. A class II restricted T-cell subset (CD4+CD45RA-), which includes memory T cells, increased with age in females. Serum IgA increased. These results support the utility of memory and naive subsets of CD8+ T cells, CD4+ T cells, and serum IgA as biomarkers for longitudinal studies. Total lymphocytes, total T cells, CD4+ T cells, and CD8+ T cells may also be useful in this species.

To develop a battery of innocuous tests measuring individual differences in the rate of biological aging, longitudinal data were gathered on 28 biochemical, physiological, and morphological characteristics of 40 adult female pigtailed macaques. The change in each variable over time, i.e., the beta coefficient of linear regression, was calculated for each animal, and a matrix of correlations among the variables was constructed. Eight variables correlated well with the first principal component of the matrix. These variables (rate of fingernail growth, blood lymphocytes, mean corpuscular hemoglobin, immunoglobulin A, and serum sodium, chloride, total protein, and creatinine) represented the best subset of the potential biomarkers analyzed to produce an index covering a range of morphologic and functional systems that change with age. A similar set representing a wider range of systems and measured over a larger fraction of the life span should provide a valid index of an individual's rate of biological aging.

The objective of our research was to establish a useful battery of innocuous tests suitable for detecting individual differences in biological aging rate in pigtailed macaques. Data were gathered from more than 60 animals of three age groups (8 to 9, 12 to 17, and 18 to 28 years olds) fed two diets differing in lipid, cholesterol, complex carbohydrate, refined sugar, and sodium chloride content. Candidate variables for an aging battery were identified in a cross-sectional analysis by performing a three-way analysis of variance (ANOVA) for the effects of age, sex, and diet on each of 72 variables. Twenty-eight variables were found to be influenced by age. By examining patterns of differences among means, 20 variables were identified that show promise of being useful, including, for example, rectal body temperature, blood albumin, immunoglobulin A, fingernail growth rate, bone thickness, and blood calcium. The set of variables used to estimate biological aging might not be identical for all age-sex classes.