Genetic differences in social behavior : relation to natural killer cell function and susceptibility to tumor development

The hypothesis that certain heritable personality traits would correlate with increased vulnerability to tumor development and reduced natural killer (NK) cell function was tested in mice selectively bred for high and low levels of aggression. This selection program produces a line of mice that fail to exhibit species typical, isolation-induced aggression, but appear socially inhibited in response to a novel partner mouse. All socially inhibited mice developed 3-methylcholanthrene-induced tumors compared with only 44% of the aggressive mice. Basal NK activity was also significantly lower among socially inhibited mice. Conversely, there were no line differences in NK activity between the aggressive line and nonselected, socially isolated mice, consistent with other unidirectional outcomes of this selective breeding program. No significant line differences were present for nonsocial measures of emotional reactivity (e.g., fearfulness) or serum corticosterone levels. These findings support the hypothesis that social "traits" may be related to immune function and tumor susceptibility.