Neonatal neutrophilia: possible role of a humoral granulopoietic factor

During the first days of life, newborn infants have leucocytosis with marked neutrophilia and a "shift to the left," the mechanism for which is as yet unknown. In an attempt to elucidate whether humoral granulopoietic factor(s) plays a role in this phenomenon, serial measurements of urinary and serum colony-stimulating activity levels were made in healthy newborn infants and normal older controls. Twenty-four-hr urine collections, serum samples, and complete blood counts were obtained from 30 full-term normal infants 24 hr and 4 days after delivery and in 13 of them on the 14th and 28th days of life as well. Specimens were assayed for their colony stimulating activity levels by their ability to stimulate bone marrow cells from C3HB mice to grow into colonies in soft agar. Elevated neutrophil, band form, and monocyte counts were found during the first day of life, which gradually decreased thereafter. Serum and urinary colony-stimulating activity levels were significantly increased (3- to 5-fold) over the controls on the first and fourth days of life, but declined to normal values by the 14th and 28th days.