A team of health psychologists zeroed in on five major human personality characteristics to understand their relationship with the immune system in a new study from the University of Nottingham and the University of California in Los Angeles.

While the results don't point to any disease-prone personalities, a propensity for socializing was associated with having a more proactive and protective immune system.

"We can't, however, say which came first," says lead author Dr. Kavita Vedhara from the University of Nottingham's School of Medicine. "Is this our biology determining our psychology or our psychology determining our biology?"

In the study, Dr. Vedhara and colleagues assembled a participant group of 121 ethnically diverse, healthy adults comprising 86 women and 35 males of an average age of 24 and an average BMI of 23.

Each participant underwent a personality test that assessed their degree of five traits: extraversion, neuroticism, openness, agreeableness and conscientiousness.

The team took note of their habits concerning exercise, smoking and drinking for control purposes and collected blood samples from each participant for gene expression analysis.

"Our results indicated that 'extraversion' was significantly associated with an increased expression of pro-inflammatory genes and that 'conscientiousness' was linked to a reduced expression of pro-inflammatory genes," says Dr. Vedhara.

"In other words, individuals who we would expect to be exposed to more infections as a result of their socially orientated nature (i.e., extraverts) appear to have immune systems that we would expect can deal effectively with infection. While individuals who may be less exposed to infections because of their cautious/conscientious dispositions have immune systems that may respond less well."

The results of the study were not related to participants' health behaviors nor to the proportions of positive and negative emotions they experienced.

The study, which puts a new dimension on epidemiological associations between physical health, personality and human longevity, was published in the journal Psychoneuroendocrinology.