Selectively high level of serum interleukin 5 in a newborn infant with cow's milk allergy

Cow's milk allergy (CMA) in the neonatal period is thought to include several clinical conditions, yet the pathophysiology remains unclear. We report here the case of a term newborn infant who showed hematochezia 36 hours after the first feeding with cow's milk formula. His serum immunoglobulin E levels were not elevated, although eosinophils were detected in the stool. Elimination of cow's milk formula resolved the symptoms, and from the clinical course and laboratory data the infant was diagnosed with CMA. The serum interleukin 5 (IL-5) (125 pg/mL) level in this patient was selectively elevated. However, serum levels of other T-helper 2 (Th2) cytokines (including IL-4 and IL-13), Th1 cytokines (including interferon γ), and proinflammatory cytokines (including tumor necrosis factor α) were not elevated. These findings suggest that, for this patient, IL-5 and eosinophils might have played a role in the development of neonatal CMA. Although this finding is reported from only 1 case, it highlights the need for serum IL-5 to be determined in more neonatal patients with CMA to further clarify the pathophysiology of this condition in the neonatal period.