title: Serum levels of the immune activation marker neopterin change with age and gender and are modified by race, BMI, and percentage of body fat.
abstract: BACKGROUND
  Neopterin, a GTP metabolite expressed by macrophages, is a marker of immune activation. We hypothesize that levels of this serum marker alter with donor age, reflecting increased chronic immune activation in normal aging. In addition to age, we assessed gender, race, body mass index (BMI), and percentage of body fat (%fat) as potential covariates.
  
  
  METHODS
  Serum was obtained from 426 healthy participants whose age ranged from 18 to 87 years. Anthropometric measures included %fat and BMI. Neopterin concentrations were measured by competitive ELISA. The paired associations between neopterin and age, BMI, or %fat were analyzed by Spearman's correlation or by linear regression of log-transformed neopterin, whereas overall associations were modeled by multiple regression of log-transformed neopterin as a function of age, gender, race, BMI, %fat, and interaction terms.
  
  
  RESULTS
  Across all participants, neopterin exhibited a positive association with age, BMI, and %fat. Multiple regression modeling of neopterin in women and men as a function of age, BMI, and race revealed that each covariate contributed significantly to neopterin values and that optimal modeling required an interaction term between race and BMI. The covariate %fat was highly correlated with BMI and could be substituted for BMI to yield similar regression coefficients.
  
  
  CONCLUSIONS
  The association of age and gender with neopterin levels and their modification by race, BMI, or %fat reflect the biology underlying chronic immune activation and perhaps gender differences in disease incidence, morbidity, and mortality.
authors.affiliation: Biology of Frailty Program, Division of Geriatric Medicine and Gerontology, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Monique E
authors.initials: ME
authors.lastname: Spencer
authors.forename: Alka
authors.initials: A
authors.lastname: Jain
authors.forename: Amy
authors.initials: A
authors.lastname: Matteini
authors.forename: Brock A
authors.initials: BA
authors.lastname: Beamer
authors.forename: Nae-Yuh
authors.initials: NY
authors.lastname: Wang
authors.forename: Sean X
authors.initials: SX
authors.lastname: Leng
authors.forename: Naresh M
authors.initials: NM
authors.lastname: Punjabi
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Walston
authors.forename: Neal S
authors.initials: NS
authors.lastname: Fedarko
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D015415:Biomarkers; D044383:Black People; D050218:Body Fat Distribution; D015992:Body Mass Index; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D019798:Neopterin / Q000097:blood*; D012737:Sex Factors; D044465:White People
chemical_list: D015415:Biomarkers; D019798:Neopterin