The use of lymphocytic choriomeningitis virus reassortants to map viral genes causing virulence.

Abstract

Lymphocytic choriomeningitis virus (LCMV) is the prototypic arenavirus. The genome consists of two single strand RNA species, L and S, with approximate molecular weight of 2.85 x 106 and 1.35 x 106, respectively [1]. Several individual strains of LCMV can be distinguished by biochemical and immunological studies. In addition, variation in the pathogenicity among LCMV strains has been reported [2, 3]. For example, C3H newborn mice inoculated with LCMV Armstrong (Arm) develop growth retardation and disordered glucose metabolism secondary to growth hormone deficiency, but infection with LCMV WE strain has no effect on growth development or blood sugar levels [4]. Adult guinea pigs resist infection when inoculated with the Arm strain but succumb when challenged with the WE strain [2, 3]. Since the genome of LCMV is segmented it is possible to generate reassortants between two different strains. We have recently obtained and characterized intertypic reassortants between the Arm and WE and the Arm and Traub strains of LCMV. Using such reassortants, monoclonal antibodies specific for the nucleoprotein (NP) and the glycoproteins (GP-1 and GP-2) of Arm and WE, and specific cDNA probes of LCMV-Arm, we have demonstrated that the small RNA segment of LCMV codes for the three major structural polypeptides [5]. Utilizing reassortant and both parental strains of virus we have shown that the perturbation of growth hormone synthesis in C3H/St mice maps to the S RNA of LCMVArm [6, Table 1] and that the L RNA of LCMV WE is important for virus replication in vivo and is associated with fatal acute disease following infection of adult guinea pigs [7, Table 1]. Both of these disease states occur independently of anti-LCMV immune responses [4, 6, 7]. Other experiments, not discussed here, show that the induction and activity of virus-specific H-2-restricted cytotoxie T lymphocytes is associated only with LCMV gene products encoded by the S RNA segment [8]. Recently we noted that LCMV reassortants with the WE/Arm or the Traub/Arm genotype caused a lethal disease following neonatal inoculation of BALB/c mice while, in contrast, parental strains or reciprocal reassortants did not. The pathogenesis of the disease which is characterized by inhibition of growth and death, is the presumed generation of interferon, causing liver necrosis. Disease and liver necrosis were prevented by the administration of a potent sheep-globulin against mouse ~ +/3 interferon (Table