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Plasma cytokine levels: Relationship to early maternal interactions in socially reared vervet monkeys (Cercopithecus aethiops sabaeus)
Mark L. Laudenslager
Lynn A. Fairbanks
Matt J. Jorgensen
Brain, Behavior, and Immunity 2006;20: e34-e35

Cytokine levels in plasma have been variously associated as risk factors for both immune and cardiovascular diseases. We tested the hypothesis that plasma cytokine levels of juvenile vervet monkeys might be related to aspects of early experience with the mother. As part of a longitudinal study in socially housed vervet monkeys (Chlorocebus aethiops sabaeus), behavioral observations of undisturbed motherinfant pairs were conducted from 5 to 12 weeks of age. This is the age when infants begin to leave the mother, and is a period that shows marked individual differences in infant behavior and maternal response. Recorded behaviors included time in contact with the mother, restraint by the mother of the infant, rejections by the mother, rates of initiating or breaking contact, and approaching or leaving between mother and infant. At 22–30 months of age the focal subjects experienced a standardized novelty challenge which involved being removed from the home cage, placed in an individual cage, and exposed to a series of novel stimuli. Blood was collected at 4 pm after a 2-h quiet period during which the subjects were left alone and undisturbed. The serum was stored at 80 C until assayed. Sixty subjects were selected for analysis of cytokine levels in addition to plasma cortisol. Although there are a large number of candidate cytokines and chemokines, we were limited to measuring those for which there were available ELISA assays with cross reactivity to the cytokines in serum collected from vervet monkeys. These cytokines included c-INF, IL-6, and TNF-a, assessed using commercial ELISA kits (U-CyTech) according to the manufacturer’s directions. Cortisol was measured by a standard RIA (DPC). Levels of inflammatory cytokines, TNF-a and IL- 6, were quite low or below the detection limits of the assays. This is related to the fact that these were healthy young monkeys with no observable infectious or inflammatory process. Post test cortisol levels averaged 52.5 ± 20.7 mg/ dl, range 12.5–120, for the entire cohort. Plasma cortisol was unrelated to any of the measures of early maternal experience but was related to agitation behaviors during the novelty test. In contrast c-INF showed consistent and significant relationships to early maternal experience. The young infants that had less contact with the mother in the second and third month of life had significantly higher plasma c-INF levels two years later as juveniles (ps < .001). The high c-INF juveniles had relatively neglectful mothers who were significantly more likely to leave their infants and less likely to restrain them. As infants, they had significantly higher rates of both approaching and leaving the mothers, suggesting that they took a more active role in exploring the environment at an early age. The extent to which these differences contribute to later health outcomes is not known at this time. These animals are part of a longitudinal study of a number of disease processes.

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