Inflammatory vulnerability associated with the rh5-HTTLPR genotype in juvenile rhesus monkeys.

Individual variation in serotonergic function is associated with reactivity, risk for affective disorders, as well as an altered response to disease. Our study used a nonhuman primate model to further investigate whether a functional polymorphism in the promoter region for the serotonin transporter gene helps to explain differences in proinflammatory responses. Homology between the human and rhesus monkey polymorphisms provided the opportunity to determine how this genetic variation influences the relationship between a psychosocial stressor and immune responsiveness. Leukocyte numbers in blood and interleukin-6 (IL-6) responses are sensitive to stressful challenges and are indicative of immune status. The neutrophil-to-lymphocyte ratio and cellular IL-6 responses to in vitro lipopolysaccharide stimulation were assessed in 27 juvenile male rhesus monkeys while housed in stable social groups (NLL = 16, NS = 11) and also in 18 animals after relocation to novel housing (NLL = 13, NS = 5). Short allele monkeys had significantly higher neutrophil-to-lymphocyte ratios than homozygous Long allele carriers at baseline [t(25) = 2.18, P = 0.02], indicative of an aroused state even in the absence of disturbance. In addition, following the housing manipulation, IL-6 responses were more inhibited in short allele carriers (F1,16 = 8.59, P = 0.01). The findings confirm that the serotonin transporter gene-linked polymorphism is a distinctive marker of reactivity and inflammatory bias, perhaps in a more consistent manner in monkeys than found in many human studies.

Prenatal influences on neuroimmune set points in infancy.

Many factors during fetal life and early infancy have been found to affect the development of immune responses in animals. This study investigated whether acute exposure of the fetal monkey to high levels of corticosteroids would also have a lingering effect on the expression of immune responses still manifest postpartum in yearling juveniles. One month prior to parturition, pregnant rhesus monkeys were administered dexamethasone for two days. Lymphocyte proliferative responses to mitogen were then examined in their offspring when they were between 1.0-1.5 years of age. In addition, cell sensitivity to corticosteroid feedback was assessed by testing the ability of a gradation of cortisol doses to inhibit proliferation. Monkeys generated from dexamethasone-treated pregnancies tended to have lower responses to concanavalin A. Further, their cells were less sensitive to in vitro incubation with cortisol, suggesting that elevated adrenal activity in vivo had downregulated hormone receptors on their cells. These findings concur with the view that steroidal hormones in utero can influence the fetal immune system, resulting in prolonged effects on immune responses after birth. The similarity of the dexamethasone condition to the clinical treatment used in obstetrical practice raises a potential concern about the widespread antenatal exposure of premature infants to steroidal drugs.

Prenatal stress and immune recognition of self and nonself in the primate neonate.

The capacity of the neonate to respond to nonself antigens was evaluated in infant monkeys born after normal and disturbed pregnancies. Mixed lymphocyte cultures were used to test the infants' proliferative responses to mitomycin-treated stimulator cells, either from a genetically unrelated animal or from a virally transformed monkey cell line. Periods of daily stress for 6 weeks in mid-late pregnancy (months 3.0-4.5) resulted in a significant decrease in proliferative responses, whereas the same stressor early in pregnancy (months 1.5-3.0) increased responses by the neonate's cells. Similar to the late stress effect, an inhibition of proliferative responses by neonatal cells was induced by dexamethasone administered for 2 days late in pregnancy at 4.5 months after conception, 1 month before term. These findings demonstrate that certain immune responses at birth are extremely sensitive to prior prenatal events. Further, the bidirectional changes indicate that there may be critical periods in gestation when the same extrinsic events have radically different effects on the fetus.

In vivo adaptation of attenuated Salmonella typhimurium results in increased growth upon exposure to norepinephrine.

Two studies were conducted to determine whether attenuated strains of Salmonella typhimurium, currently being investigated as possible vectors for mucosal vaccines, are able to respond to norepinephrine (NE). Bacteria were tested for NE responsiveness before and for 1 week after passage through juvenile rhesus monkeys. NE significantly increased the growth of the attenuated bacteria after being shed from the animal, but not before animal infection. Follow-up in vitro tests were performed by passaging the bacteria in Lauria-Bertani (LB) broth with or without selective antibiotic for the attenuation insert and supplementing with NE. NE increased the growth of bacteria passaged in LB broth with no selective antibiotic, but not in bacteria passaged in LB broth with selective antibiotic. These results show that the attenuated bacteria assumed to be safe for use as a vaccine are able to respond to environmental stimuli, such as NE, and change their characteristics. The results suggest that there may be problems with the stability of attenuated bacteria used as vectors for mucosal vaccines.

Growth and development following prenatal stress exposure in primates: an examination of ontogenetic vulnerability.

Previous studies have found that stressful events during pregnancy can influence the developing fetus, resulting in attentional and neuromotor problems. This prospective study examined whether periods of vulnerability exist for neurobehavioral impairments associated with prenatal stress, using a nonhuman primate model. Twenty-eight rhesus monkey infants were born to mothers in 3 groups: (1) early gestation stress involving mild psychological stress from gestational days 45-90, (2) mid-late gestation stress from days 90-145, and (3) undisturbed controls. Infants were separated from their mothers on days 4, 9, 15, and 22 (+/- 1) postpartum for growth and neurobehavioral assessments. Results indicated that infants from the early gestation stress condition weighed less than infants from mothers stressed during mid-late gestation. Moreover, whereas both groups scored lower than controls on measures of attention and neuromotor maturity, early gestation stress was associated with more pronounced and more pervasive motor impairments than mid-late gestation stress. These results suggest sensitivity to prenatal stress effects peaks during early gestation, tapering off during mid-late gestation. Clarifying the period of greatest vulnerability to prenatal stress moves toward elucidating the underlying mechanism for prenatal stress effects and may lead to more successful intervention and/or prevention.

Prenatal stress alters brain biogenic amine levels in primates.

In this study, we assessed behavioral responses to social separation at 8 months of age and cerebrospinal fluid (CSF) concentrations of biogenic amines and metabolites at 8 and 18 months of age in 12 rhesus monkeys derived from either stressed or undisturbed pregnancies. Compared to controls from undisturbed pregnancies, prenatal stress-derived monkeys had higher concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG), and 3,4-dihydroxyphenylacetic acid in CSF than controls. Norepinephrine and MHPG response to stress were both correlated between 8 and 18 months of age. There were few group differences in behavior during social separation; however, several behavioral differences between groups were found when monkeys were reunited with cage mates. Prenatally stressed monkeys spent more time clinging to their surrogates and exploring (including eating and drinking), while controls showed more locomotion and social play with their cage mates. Collectively, our findings suggest that chronic unpredictable psychological stress during pregnancy has long-lasting effects on noradrenergic and dopaminergic activity and behavior in the offspring of gestationally stressed primate mothers.

Prenatal endocrine activation alters postnatal cellular immunity in infant monkeys.

Cellular immune responses were evaluated in 35 infant rhesus monkeys generated from two types of pregnancy conditions. Pregnant females were administered either saline or adrenocorticotropic hormone (ACTH) for 2 weeks between Days 120 and 133 postconception, approximately 1 month before parturition. After birth, lymphocytes obtained from infants in the ACTH condition failed to respond as readily to allogeneic cells in mixed lymphocyte cultures, proliferated less to Con A, exhibited lower suppressor function following stimulation with Con A, and showed lower cytolytic activity against target cells. For some measures, the prenatal effect was observed more consistently in male infants. Differences were evident with these in vitro immune assays through 6 months of age, indicating that acute disturbance during the prenatal period can have lingering effects on postnatal immunity.

Effects of early rearing environment on immune responses of infant rhesus monkeys.

In animals, perturbations of the rearing environment have been shown to alter behavior, cognition, and physiology, including immune responses. In order to evaluate the effect of early rearing conditions on the development of immune responses in the infant primate, several immunological measures were assessed in rhesus monkey infants, nursery-reared (NR) or mother-reared (MR), from birth to 2 years of age. Rearing in the absence of the mother affected several aspects of cellular immunity. NR monkeys had significantly lower proportions of CD8 cells and lower natural killer cell activity than did MR monkeys. In contrast, their lymphocyte proliferation responses to mitogen stimulation were higher than those of MR monkeys. An attempt to behaviorally rehabilitate the NR infants at 1 year of age did not result in a recovery of normal immune responses. This study indicates that abnormal early rearing may have long-lasting effects on the immune system, which could have health consequences later in life.

Early rearing conditions alter immune responses in the developing infant primate.

The influence of early rearing conditions on immunologic development was investigated in infant monkeys. Lymphocyte proliferation, natural killer cell activity, and antibody responses to tetanus vaccination were compared in 30 rhesus monkeys reared under five different conditions. Lymphocyte responses to two mitogens (concanavalin A and pokeweed) were significantly increased in infants from disturbed rearing conditions compared with control infants that had been reared in an undisturbed manner by their mothers. The largest increases occurred in nursery-reared monkeys that had been fed Similac infant formula. The nursery-reared monkeys also tended to show lower natural killer cell activity, but there were no significant differences in response to vaccination. These findings support other research indicating that psychologic and nutritional aspects of the early rearing environment may have long-lasting effects on some, but not all, immune responses in the developing infant.

Endocrine activation mimics the adverse effects of prenatal stress on the neuromotor development of the infant primate.

Pregnant female rhesus monkeys were exposed to a 2-week period of adrenocorticotropic hormone (ACTH) to determine whether it would affect the early neuromotor development of their fetuses in a manner similar to that observed after psychological stressors. During the first month after birth, infants were tested on two occasions with a modification of the Brazelton Newborn Behavioral Assessment Scale. Infants derived from ACTH-treated pregnancies showed early impairments in motor coordination and muscle tonicity and shorter attention spans as compared to controls. In addition, on a temperament rating scale, infants from the ACTH condition were more irritable and difficult to console. These findings indicate that a delimited period of endocrine activation during pregnancy can have an adverse effect on infant neurobehavioral development, like that of prenatal stress.

Maternal influences on body temperature in the infant primate.

The following study investigated the diurnal variation in body temperature of the young monkey infant and assessed the role that the mother plays in the development of the temperature rhythm. Using an implantable biotelemetry system, core body temperature and motoric activity were evaluated in maternally-reared and hand-reared rhesus monkey infants across the first several months of life. Our results indicated that the nocturnal temperatures of hand-reared infants are lower than those of mother-reared infants at one month of age, and that there are persistent differences in the orientation and shape of the diurnal temperature rhythm. The initial thermal challenge and the prolonged rhythm shift may have implications for the normal development of several physiological systems in the hand-reared infant monkey.

Influence of early rearing on lymphocyte proliferation responses in juvenile rhesus monkeys.

Lymphocyte proliferation responses and natural killer cell activity were evaluated in 35 juvenile rhesus monkeys derived from five different rearing conditions. Nursery-reared monkeys had proliferation responses which were significantly higher than those of mother-reared subjects. Reexamination of the nursery-reared monkeys 1.5 years later indicated that an abnormally high response to concanavalin A was still evident at 2.5 years of age, but both PHA and PWM responses had shown an age-appropriate decrease into the normal range for this species. Proliferation responses in monkeys that had been weaned early from their mothers at 6 months of age were also higher than values for control monkeys that remained with their mothers, but below those of the nursery-reared monkeys. In contrast, monkeys that had received multiple separations from the mother between 3 and 7 months of age showed lymphocyte proliferation responses that were below normal. These results indicate that early rearing conditions can have a lasting effect on certain immune responses in the developing primate.