Thrombopoietin in human milk.

Abstract

Several hematopoietic cytokines, including granulocyte colony-stimulating factor (G-CSF), macrophage (M)-CSF, GM-CSF, and erythropoietin (EPO), have been substantially detected in human milk [1,2]. As the neonatal gastrointestinal tract has less proteolytic activity than that of adults, hematopoietic factors can survive the environment of the neonatal gut [1]. Furthermore, receptors for EPO and G-CSF were recently discovered in the fetal intestine [2,3], leading to a hypothesis that such cytokines are absorbed intact through specific receptors into the circulation and exert a developmental function in neonates [2,3]. Thrombopoietin (TPO), the ligand for cytokine receptor Mpl, is the primary physiological regulator of platelet production and plays a pivotal role in promoting the proliferation and maturation of megakaryocytic progenitors and megakaryocytes [4]. This mechanism also operates in term and preterm neonates, although preterm counterparts have an impaired ability to increase TPO levels in response to thrombocytopenia [5]. It remained to be elucidated whether TPO is present in human milk, and what, if any, role TPO in human milk plays in infantile thrombopoiesis. As a first step, we investigated TPO concentration in human colostrum/milk using a sensitive enzymelinked immunosorbent assay (ELISA) kit. Samples of milk were collected from healthy women who delivered their infants at Nishi-Kobe Medical Center from July to October 2000 (Table 1), after obtaining the informed consent of the participants. Human milk was collected from mothers, aged 18-41 years, who delivered prematurely (≤37 weeks gestation; n = 2) or at term (n = 10). Five samples of colostrum were obtained within 5 days, 5 samples of transitional milk at 6 to 30 days, and 2 Thrombopoietin in Human Milk Kousaku Matsubara,a Takashi Kato,b Hiroshi Miyazakib