Lowly status proves infectious in monkeys.

Experimental disruptions of the social life of macaque monkeys have yielded intriguing, but ultimately puzzling, clues to the relationship between mind and physical health.

Primates at the bottom of the social "pecking order" display a particularly keen susceptibility to infection by a virus that causes coldlike symptoms, reports a scientific team headed by psychologist Sheldon Cohen of Carnegie Mellon University in Pittsburgh. This susceptibility cannot be attributed to such characteristics of low-status monkeys as low body weight, a penchant for submissive behavior, and declines in some measures of immune function, according to Cohen's group.

In contrast, monkeys exposed to the stress of persistent membership changes in their social groups proved no more likely to develop a viral infection than those in stable groups. This result appears to contradict previous evidence that such stress weakens immune responses in macaques (SN: 10/10/92, p. 237). It coincides, however, with indications that stressful experiences provoke and worsen symptoms in infected humans but do not alter a person's chances of getting infected in the first place.

"Social stress [in macaques] was not associated with susceptibility to infection," the researchers report in the May-June Psychosomatic Medicine. "However, animals with lower social status were at higher risk than high social status animals."

Macaques provide a good animal model for researchers seeking insights into the relationship between the human immune system and psychological and social factors, the researchers add.

Cohen and his coworkers studied 60 male macaques housed in five-member groups for 15 months. Half of the monkeys were assigned at random to an unstable group, in which three or four members changed places with individuals from other unstable groups on a monthly basis. The rest of the animals lived in groups that maintained a stable membership throughout the study.

Rankings of social status for each monkey depended on the animal's ability to elicit submissive behaviors from others and on the proportion of its daily activity that involved submissive displays.

After month 9, the researchers obtained measures of immune cell function and of several stress hormones every 2 to 3 months.

At the beginning of month 15, each animal was sedated and exposed to a coldlike virus in a solution applied to its nostrils. Nasal secretions were collected 2 and 4 days later and analyzed for signs of infection.

Of the 12 monkeys ranked lowest in social status, 8 became infected, the scientists report. Infections also occurred in 4 of the 12 monkeys who were second-lowest in social status. For animals on the remaining three rungs of the social ladder, only one at each position developed an infection.

Low-status monkeys exhibited lower body weights, greater surges in stress hormones when housed in unstable groups, and drops in immune cell function. These trends could not account statistically for their surplus of infections, according to the investigators.

Further research on the monkeys may require more sophisticated measurements of hormonal and immune responses to yield a clearer picture of their relationship to social status and stress, writes psychologist Christopher L. Coe of the University of Wisconsin-Madison in an accompanying comment.

Still, the new study adds to evidence (SN: 8/31/91, p. 132) that psychological factors influence some viral infections. Coe suspects that stress may block the recruitment of immune cells to sites of infection.