Abstract
In humans, neutrophil to lymphocyte ratio (NLR) has been used as a clinical tool in diagnosis and/or prognosis of a variety of cancers and medical conditions, as well as in measuring physiological stress over time. Given the close phylogenetic relationship and physical similarities between humans and apes, NLR may similarly be a useful diagnostic tool in assessing chimpanzee health. Only one study has examined NLR in apes, reporting that NLR increased with age and was affected by body-mass index and sex. In the current study, we examined changes in NLR data from longitudinal health records for 443 chimpanzees in two captive chimpanzee populations. Using these data, we analyzed intra-individual changes and inter-individual differences in NLR as a function of age, rearing history, and sex. Contrary to previous studies in humans and the one previous study in chimpanzees, NLR values did not change over a 10-year timespan within individual chimpanzees. However, cross-sectional comparisons revealed a significant quadratic relationship between age and NLR, with the highest values during mid-life (20–30 years of age) and the lowest values in younger and older individuals. Additionally, males and mother-reared individuals had higher NLR than females and nursery-reared chimpanzees, respectively. Lastly, males and those with higher NLR values died at younger ages. These findings suggest that NLR may be useful as a predictor of longevity in chimpanzees. However, given the complexities of these relationships, more research is needed to determine the utility of NLR as a diagnostic health tool for chimpanzees.
Highlights
Neutrophil to lymphocyte ratio (NLR) is often used as a biomarker of inflammation
Consistent with previous research in humans and chimpanzees, we predicted that elevated NLR would be exhibited by older individuals, males, and nursery-reared chimpanzees, and that higher NLR values would be associated with younger ages at death
We were able to expand upon these previous findings by using a larger sample size (N = 425 vs. 39), including chimpanzees spanning a larger age range (2–58 years old vs. 3–31 years), with different rearing histories, and using average NLR over several years, rather than an NLR value taken at one point in time
Summary
Neutrophil to lymphocyte ratio (NLR) is often used as a biomarker of inflammation. The measurement of NLR is obtained through differential cell counts assayed from blood by dividing the number of neutrophils by the number of lymphocytes. Males had higher NLR than females, but NLR increased more strongly with age and BMI in females than in males These results are generally consistent with the human literature showing a positive relationship between age and NLR in healthy subjects. Nursery rearing affects lymphocyte proliferation responses in 2-year-old monkeys, which alters immune function and increases susceptibility to infectious diseases later in life [35]. Just one study has examined the relationship between rearing and blood biomarkers of health in chimpanzees [38], finding no differences between mother- and nursery-reared chimpanzees (aged 6 months– 10 years, N = 46) in hematology or serum chemistry values. Consistent with previous research in humans and chimpanzees, we predicted that elevated NLR would be exhibited by older individuals, males, and nursery-reared chimpanzees, and that higher NLR values would be associated with younger ages at death
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