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.