Objective: A pattern of clinical, behavioral, and experimental findings sug
gests that individual differences in aggressive behavior may be related to
immunologic processes. We evaluated two conflicting models of the relations
hip: 1) A positive association stems from an adaptive mechanism protecting
aggressive individuals from increased exposure to immune stimuli and 2) a n
egative association is due to potential immunosuppressive effects of high t
estosterone levels. Methods: We investigated the models using enumerative m
easures of cellular and humoral immunity in a sample of 4415 men aged 30 to
48 years who were interviewed and underwent a medical examination. Results
: Analysis revealed positive land curvilinear) associations between aggress
ive behavior and enumerative measures of helper/inducer and suppressor/cyto
lytic T lymphocytes and B lymphocytes. The aggression-immunity relationship
was independent of testosterone level, age, current health status, and neg
ative health behaviors and was most pronounced for helper/inducer T cells.
There was no evidence of a negative association between testosterone and an
y immune measure. Conclusions: In a large sample of men, individual differe
nces in aggressive behavior were positively associated with enumerative mea
sures of cellular immunity.