TABLE 1.

Wild-type MVs (strains IV, JW, Bcl94, and FV93) induce 10- to 80-fold less IFN-α/β than do the attenuated Edmonston, Moraten, or Vero cell-adapted IV, JW, Bcl, and FV virus strains^a

Virus strain	IU of IFN/ml of supernatant
	Expt 1	Expt 2
NI	250	120
Edmonston	2,000	4,000
Moraten	5,000	10,000
JW	120	120
IV	120	250
Bcl94	120	120
FV93	120	250
IV-Vero	10,000	1,250
JW-Vero	2,500	10,000
Bcl-Vero	1,250	2,000
FV-Vero	1,250	2,000

^aVirus-free supernatants from cells infected with different MV strains were assayed for the biological activity of IFN-α/β. JW and IV are wild-type MV isolates passaged solely on human PBMC, while Bcl94 and FV93 were isolated and passaged on the B958 marmoset cell line. The Edmonston and Moraten MV strains are highly attenuated and were passaged on the monkey Vero cell line. IV-, JW-, Bcl-, and FV-Vero are the wild-type viruses passaged 10 times on Vero cells. NI, noninfected cells.