Immunological development of preterm infants in early infancy
To evaluate the immunological development of preterm infants, especially in early infancy, we examined the serum cytokine levels and the expression of Th2 and Th1 chemokine receptors, CCR4 and CCR5, on days 0, 14 and 28 in 16 low birth weight infants (1720·38 ± 502·80 g) born at less than 37 (33·63 ± 3·29) weeks of gestation. Using an enzyme‐linked immunosorbent assay (ELISA), serum interleukin (IL)‐4 levels exhibited an increase on day 14, but decreased to the initial level on day 28 (P < 0·05). The significant elevation of serum transforming growth factor (TGF)‐β levels was confirmed on day 14 (P < 0·05) but decreased to the initial level on day 28 (P < 0·05). The expression of CCR4 and CCR5 were examined using reverse transcription‐polymerase chain reaction (RT‐PCR) and flow cytometric analysis. The RT‐PCR confirmed the expression of CCR5‐mRNA soon after birth, while there was no expression of CCR4‐mRNA. Thereafter, the expression of CCR4‐mRNA increased significantly and reached the level of CCR5‐mRNA expression on day 28 (P < 0·05). Flow cytometric analysis, however, revealed that the expression levels of both CCR4 and CCR5 were low at birth. Thus, CCR4+ CD4+ cells were significantly increased from days 0–28 (P < 0·05), while CCR5+ CD4+ cells were not. Increased IL‐4 and TGF‐β synthesis as well as increased CCR4+ CD4+ cells suggest that, under extra‐maternal circumstances, there is a shift in bias toward Th2 responses even in preterm infants soon after delivery, while they may be capable of developing Th1 mediated responses soon after birth.