Genetic analysis of in vivo-selected viral variants causing chronic infection: importance of mutation in the L RNA segment of lymphocytic choriomeningitis virus

Abstract

Viral variants with different biological properties are present in the central nervous systems (CNS) and lymphoid tissues of mice persistently infected with lymphocytic choriomeningitis virus (LCMV). Viral isolates from the CNS are similar to the original Armstrong LCMV strain and induce potent virus-specific T-cell responses in adult mice, and the infection is rapidly cleared. In contrast, LCMV isolates derived from spleens of carrier mice cause persistent infections in adult mice. This chronic infection is associated with low levels of antiviral T-cell responses. In this study, we genetically characterized two independently derived spleen variants by making recombinants (reassortants) between the spleen isolates and wild-type (wt) LCMV and showed that the ability to persist in adult mice and the associated suppression of T-cell responses segregates with the large (L) RNA segment. In addition, we analyzed a revertant (isolated from the CNS) derived from one of the spleen variants. By comparing the biological properties of three reassortants that contained the same S segment but had the L segment of either the original wt Armstrong LCMV, the spleen variant derived from it, or the CNS revertant derived from the spleen variant, we were able to show unequivocally that biologically relevant mutations occurred in the L segment not only during generation of the spleen variant from wt LCMV but also in reversion of the spleen variant to the wt phenotype. Thus, our results showed that (i) genetic alterations in the L genomic segment were involved in organ-specific selection of viral variants, and (ii) these mutations profoundly affected the ability of LCMV to cause chronic infections in adult mice.

Virus-induced immunosuppression: immune system-mediated destruction of virus-infected dendritic cells results in generalized immune suppression

“…Clone 13 differs from its parent virus Armstrong at only two amino acid positions, one in the virus glycoprotein GP-1 and the other in the putative viral polymerase L (56,58). While the polymerase change contributes to the immunosuppressive phenotype (3,37), likely by giving clone 13 a replicative advantage over Armstrong, only the phenylalanine (Armstrong) to leucine (clone 13) change in GP-1 is consistently associated with the immunosuppressive phenotype (1,56). There is strong evidence indicating that GP-1 is the virion attachment protein that mediates binding to cell surface receptors for LCMV (9,51,67).…”

“…The virus isolates used are closely related in that the immunosuppressive LCMV isolate (clone 13) was derived from the spleen of a mouse persistently infected from birth with the nonsuppressive LCMV Armstrong 53b isolate (2), and differs from it at only two amino acid positions, amino acid 260 in the virus glycoprotein GP-1 and amino acid 1079 in the viral polymerase protein, L (1,56,58). Sequence analysis of a panel of independently-isolated immunosuppressive variants derived from Armstrong-infected mice has shown that only the amino acid change in GP-1 is consistently associated with the immunosuppressive phenotype (1,56), while reassortant analysis suggests that the L RNA sequence also affects the biological properties of the virus (3,37).…”

DNA vaccination against persistent viral infection

“…CTL assays. Primary and secondary LCMV-specific CTL responses in spleens and lymph nodes were determined by a 6-h 51 Cr release assay as described previously (4,5).…”

Molecular determinants of macrophage tropism and viral persistence: importance of single amino acid changes in the polymerase and glycoprotein of lymphocytic choriomeningitis virus

“…The outcome of a viral infection depends on a critical balance between the extent of viral spread and replication and the magnitude of the host's immune response. We have been studying infection of mice with lymphocytic choriomeningitis virus (LCMV) as a model system to understand the host and viral determinants that lead to viral clearance or persistence (2,4,5,20). Infection of immunocompetent adult mice with the Armstrong strain of LCMV induces a potent antiviral T-cell response, and virus is eliminated within 2 weeks.…”