Neonatal eosinophils possess efficient Eotaxin/IL-5- and N-formyl-methionyl-leucyl-phenylalanine-induced transmigration in vitro.

The majority of premature infants develop eosinophilia and abnormalities in eosinophil trafficking during the first period of postnatal life. We therefore thought to assess the ability of neonatal eosinophils to transmigrate in vitro toward chemotactic stimuli mimic either bacterial infections, or to allergic inflammation in vivo, and to compare the results with eosinophils in adults. We used an in vitro transmigration method and the chemotactic stimuli N-formyl-methionyl-leucyl-phenylalanine (fMLP) or a combination of IL-5 and eotaxin. The expression of the adhesion-promoting molecule CD11b and the fMLP receptor were assessed by flow cytometry. Both the fMLP- and IL5/eotaxin-induced eosinophil transmigration capacity was significantly more efficient in neonates than in adults (p < 0.0001 and p < 0.0002, respectively). The fMLP-induced up-regulation of CD11b on eosinophils was significantly (p < 0.0003) higher in neonates compared with that in adults. We also assessed a significant (p < 0.0001) higher expression of the fMLP receptor on resting eosinophils in neonates compared with that in adults. The integrated impact of increased transmigration capacity, fMLP receptor expression, and CD11b expression on eosinophil by bacterial peptide fMLP suggests that neonatal eosinophils possess the potential to play an alternative role compared with eosinophils in adults.