This definition appears rarely
Bone marrow-enhancing factor (B-EF) is the spontaneous product of whole bone marrow cells cultured in serum-free medium for a short term (24–48 hr). The factor is prepared by ultrafiltration of BMC supernates to yield a preparation with a MW of greater than 10,000. Production of the factor is not dependent upon antigenic or mitogenic stimulation of BMC, but is inhibited by treatment of BMC with cycloheximide.