Acute shift in immune response to microbial activators in very-low-birth-weight infants.

Investigation of lymphocyte activation in vitro to microbial pathogens was undertaken in very-low-birth-weight infants during the first 2 weeks of life. Twenty-three infants with birth weights less than 1500 g were studied on day 1. Normal adults (n = 23) and cord blood from seven full-term infants were used as controls. Longitudinal studies were also carried out on seven of the 23 infants 2 weeks following delivery. Results indicated that lymphocyte responses of very-low-birth-weight infants on day 1 of life were significantly greater than those of both adult controls and full-term infants, particularly to Haemophilus influenzae, Staphylococcus epidermidis and Staphylococcal protein A. In contrast, response to the T cell mitogen phytohaemagglutinin (PHA) was significantly less in very-low-birth-weight infants than in adult controls and full-term infants. The seven very-low-birth-weight infants studied showed a down-regulation of immune response in the 2 weeks following birth, such that responses on day 14 were significantly less than those on day 1 for the same activators. This shift in immune response appears to have important implications for the immune development and host defence in the post-natal period.