Regulation of Circulating Hematopoietic Stem/Progenitor Cells in Preterm Infants with Septicemia

Preterm infants are at high risk of developing severe sepsis. Circulating hematopoietic stem and progenitor cells (HSPCs; CD45(+) CD34(+)) have been suggested to play a vital role in the host immunological defense against invading pathogens. The objectives were to investigate the regulation of circulating HSPCs in preterm infants during infection episodes, and to assess the relationship of CD45(+) CD34(+) cells with immunological mediators and differential leukocyte populations. First, we conducted a cross-sectional case-control study comparing these parameters among infected infants (n = 23), gestational and postnatal age-matched noninfected infants (n = 46), and ``healthy'' control (CTL) infants (n = 12). Second, we investigated the longitudinal change of CD45(+) CD34(+) cell concentrations in infected infants before, during, and after an infection episode, and compared them with the other two groups. Our cross-sectional results showed that CD45(+) CD34(+) cell count and percentage were significantly reduced in infected infants during systemic infection, compared with the noninfected or CTL infants. There were significant positive correlation between levels of CD45(+) CD34(+) cells and lymphocytes or monocytes, and significant negative correlation between CD45(+) CD34(+) cells and neutrophils or interleukin (IL)6 in infected infants. Longitudinal analysis showed that changes of CD45(+) CD34(+) cells at the onset of sepsis relative to levels 1 week prior and 1 week postsepsis in infected infants were significantly different from those changes in the corresponding time points for the other two groups. Our findings suggested that circulating HSPCs were dynamically regulated during septicemia and could play an important role in the defense mechanism, plausibly contributing to replenishment of leukocytes during sepsis in preterm infants.