Bone marrow colony-stimulating activity of sera in infectious mononucleosis.

From 44 to 100% of sera from patients with infectious mononucleosis exhibited the capacity to stimulate colony formation in vitro by mouse bone marrow cells. The proportion of sera with colony-stimulating activity was highest in patients with a short fever period and developing low Paul-Bunnell titres. Patients with a more severe course of the disease generally displayed no, or only weak, colony-stimulating activity in their sera, and also had higher Paul-Bunnell titres. The level of serum colony-stimulating activity tended to fall in the convalescent stages of the disease.