TABLE 1.

Loss of GFP expression of MHV-SGFP and increase of viral titers during virus passaging^a

Passageb	MHV-SGFP A		MHV-SGFP B
	% GFP	TCID50	% GFP	TCID50
P1	95	1.0 × 105	98	1.5 × 105
P2	50	6.8 × 105	80	1.0 × 106
P4	1	2.2 × 106	2	1.5 × 106
P6	0	6.8 × 106	0	1.0 × 107

^a% GFP, infected cells were detected by immunofluorescence microscopy for MHV infection by using an anti-MHV serum and the red fluorescent Cy5 secondary antibody. The percentage of green fluorescent over red fluorescent (% GFP) cells was determined.

^bLR7 cells were infected with MHV-SGFP clones A or B, passages 1, 2, 4, and 6.