Effects of age,rearing, and separation stress on immunoglobulin levels in rhesus monkeys

The study reported here examined the effect of different rearing conditions and psychological stress on immunoglobulin levels in rhesus monkey infants. In the first experiment, 24 rhesus neonates were placed in one of the three following rearing conditions: Separated from their mothers and reared in the laboratory nursery; kept with their biological mothers; or removed at birth from their biological mothers and cross-fostered to adoptive rhesus mothers. Plasma samples were obtained from the nursery-reared infants immediately after birth and at weekly intervals for the next 30 days. Samples were also obtained from mother-reared and foster-reared infants on days 15 and 29. All samples were tested for IgG and IgM levels. The results indicated that neither rearing nor diet affected Ig levels. IgG levels were highest at birth and decreased progressively for the first 30 days, suggesting that placental transfer of maternal IgG is the critical determinant of IgG levels in primate infants as in humans. IgM changes were also similar to those in human infants: Low levels at birth, a significant increase from birth to day 15, and a moderate decline from day 15 to day 30. When IgG levels and IgM levels were correlated across the first month, many significant correlations were found which were consistent with human data relating both infant IgG and IgM levels to infant maturation. In the second experiment, 11 of the previously tested nursery infants were subjected to four consecutive social separations from peer groups at 6 months of age. Plasma samples were obtained before and after the first and fourth weeks of separation and tested for IgG and IgM levels. Small but significant decreases in both immunoglobulins were detected after 4 days of separation, particularly on the fourth week.