Abstract
T-cells express two surface antigen isoforms that represent two different maturational
stages. Naive T-cells express CD45RA and memory T-cell express CD45RO. Naive T-cells
can convert to memory T-cells after antigenic exposure. We hypothesized that naive
T-cell expression would be high in healthy newborns compared with adults and that
memory T-cell expression would remain low in septic newborns. The expression of naive
and memory T-cells was examined using flow cytometry on peripheral blood samples from
15 newborn infants (gestational age 36 ± 1 weeks) with clinical or culture positive
sepsis, cord blood samples from 20 healthy newborn infants (gestational age 37 ± 1
weeks) and peripheral blood samples from 24 healthy adults. Both healthy and septic
newborns demonstrated a significantly higher percentage of naive T-cells compared
with adults (57 ± 2%, 67 ± 4% vs. 40 ± 2%; P < 0.05). Expression of memory T-cells was significantly lower in healthy newborns
than adults (8 ± 1 % vs. 46 ± 2%, P < 0.0001). However, septic newborns had a significantly higher percentage expression
(14 ± 2% vs. 8 ± 1%, P < 0.01) and absolute number of memory T-cells (812 ± 112/mm3 vs. 600 ± 222/mm3 P < 0.01) than healthy newborns. The percentage expression and absolute number of memory
T-cells remained persistently high in septic newborns compared with healthy newborns
even after they had completed a full course of antibiotics and recovered from sepsis.
The marked predominance of naive T-cells in newborns is consistent with our hypothesis
that T-cell immune system is immature at birth. However, newborn infants are capable
of increasing expression of memory T-cells in response to sepsis.
Keywords
Memory T-cells - naive T-cells - neonatal sepsis - newborn infants
