Difference of two new LCMV strains in lethality and viral genome load in tissues.

More than 30 strains of lymphocytic choriomeningitis virus (LCMV) have been isolated from mice, hamsters and humans in the United States, Europe and Japan. Experimentally infected mice exhibit different clinical signs and lethality depending on a combination of LCMV epitope peptides and host major histocompatibility complex (MHC) class I molecules. This study examined the pathogenicity, clinical signs and lethality, of two new LCMV strains (BRC and OQ28) using three inbred mouse strains with different genetic backgrounds having different H-2D haplotypes. Strain OQ28 (OQ28) infected mice exhibited clinical signs and lethality, whereas strain BRC (BRC) infected mice showed no clinical signs of infection. The viral genome load in tissues of C57BL/6 mice infected with two strains was determined using one-step real time RT-PCR. In C57BL/6 mice, higher levels of OQ28 viral genome load were detected in all tissues rather than were present in BRC infected mice. The viral genome load in lungs of both virus strains remained higher levels than in other tissues at 28 days post infection. Comparing sequences of the three LCMV epitope peptide regions revealed one non-conservative amino acid substitution codon in OQ28 and two amino acid differences in BRC. These results suggest that the varied pathogenicity and viral genome load of LCMV strains are not based only on differences in the host MHC class I molecule.