Depressed phytohemagglutinin and concanavalin A responses in premature infants

Evaluation of lymphocyte phenotype and phytohemagglutinin response in healthy very low birth weight infants

Sixteen healthy very low birth weight infants (VLBWI) were studied in a serial fashion over a 3-week period. Subjects were evaluated for lymphocyte phenotype, phytohemagglutinin (PHA) response, and metabolic status including weight, blood urea nitrogen, creatinine, albumin, pH, calcium, phosphorus, and ammonia. Lymphocyte phenotype determination showed a decreased proportion of CD3+ cells (66.8 +/- 10.4 vs 75.9 +/- 6.1, P less than 0.02) in VLBWI. When subsets of the CD4+ population were examined, VLBWI had a lower proportion of CD4+/CD29+ cells (8.2 +/- 5.8% vs 23.5 +/- 8.0%, P less than 0.0001) than adults and a higher proportion of CD4+/CD45R+ cells (35.6 +/- 12.4% vs 22.2 +/- 7.4%, P less than 0.03). The CD4+ subsets in VLBWI were similar to those seen in term infants. The peak PHA response in VLBWI was greater than that of adults (P less than 0.01). There was little change in the immune measurements over the 3-week study period. There were no strong correlations between any of the immunological measurements and the metabolic measurements except that the proportion of CD8+ cells increased with birth weight. Our findings demonstrate that immune measurements in healthy VLBWI differ from values found in adults but are similar to those of full-term infants. Lower proportions of the CD4+/CD29+ cells (the helper/inducer subset for antibody production) may contribute to some of the differences in immune function reported in neonates.

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.

Normal lymphocyte responses to mitogens in term and premature neonates following normal and abnormal intrauterine growth

Cord blood lymphocyte responses to a panel of four mitogens were studied in 242 neonates using a whole blood technique. The patient population was divided into five gestational-age groups: 20-27.9, 28-32.9, 33-37.9, 38-41.9, and 42-44 weeks. Neonatal lymphocytes undergo a continuous reduction in proliferative responsiveness to the polyclonal ligands phytohemagglutinin (PHA) and concanavalin A (Con A) as gestation progresses from 20 to 44 weeks postconception. This is consistent with their change in unstimulated in vitro blastogenesis which when measured over the same developmental period is greatest in more immature neonates. Neonatal lymphocyte proliferative responsiveness to pokeweed mitogen (PWM) and staphylococcus protein A (SpA), however, was unrelated to gestational age. The influence of intrauterine nutritional deprivation on lymphocyte proliferative responses was studied in clinically uninfected newborns and compared to gestational age-matched controls with a normal nutritional status. Intrauterine nutritional deprivation was not associated with a decrease in mitogen-induced lymphocyte proliferation. Further, we explored the influence of several perinatal clinical settings commonly associated with fetal distress on cord blood lymphocyte responses to mitogens. Although perinatal stress in the form of low Apgar scores, meconium-stained amniotic fluid, and prolonged rupture of the amniotic membranes was not related to differences in mitogen induced lymphocyte proliferation, mode of delivery was. Cesarean section delivery as compared to vaginal delivery was associated with a significantly greater PHA-, Con A-, and SpA-induced neonatal lymphocyte response. Several alternative explanations for this finding are explored. Lastly, the purified protein thymosin fraction 5 was not associated with alteration in either neonatal or adult mitogen-induced lymphocyte proliferation.

Ontogeny of T-cell mitogen response in Lewis rats: I. Culture conditions and developmental patterns

Spleen and thymus cells from female Lewis rats 2 to 220 days old were cultured with phytohemagglutinin (PHA) or Concanavalin A (Con A). The optimal dose of Con A for mitogenesis ranged from 1 microgram/ml for suckling rats to 125 micrograms/ml for adult rats. Thymus cells differed from spleen cells in that they required 72 hours for maximum thymidine incorporation; whereas spleen cells attained maximum incorporation within 48 hours. Thymidine uptake in unstimulated spleen cell cultures was high in the neonate and decreased with age. Maximum splenic cell responses to Con A increased from very low levels in the 2-day old to adult levels by 3 weeks coincident with weaning. Maximum PHA responses of splenocytes matured more slowly, reaching adult levels by 8 weeks. Thymus cell responses to Con A and PHA were mature from birth.