The art of survival during viral persistence.

Stohlman, Stephen A; Ramakrishna, Chandran; Tschen, Shuen-Ing; Hinton, David R; Bergmann, Cornelia C

Central nervous system infection by the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in chronic demyelination characterized by viral persistence in the absence of infectious virus. CD8(+) T cells inhibit acute viral replication via cell type-specific effector mechanisms. Perforin-mediated cytolysis controls virus in microglia/macrophages and astrocytes, whereas interferon (IFN)-gamma regulates viral replication in oligodendroglia. JHMV infection of antibody-deficient mice confirmed a primary role of cellular immunity and a redundant role for humoral immunity during acute infection. However, infectious virus reactivates in antibody-deficient mice following viral clearance. This observation suggests that virus-specific T cells in the central nervous system are unable to control viral persistence. Reactivation in antibody-deficient mice is not associated with increased T-cell infiltration, but is prevented via transfer of neutralizing antibody. A vital role for humoral immunity during persistence is supported by the accumulation and retention of virus-specific antibody secreting cells following clearance of infectious virus. Thus, cell-mediated immune responses control acute infection, whereas humoral immunity maintains viral persistence. Therefore, although the central nervous system provides an environment for prolonged retention of both T cells and plasma cells, plasma cells are critical in maintaining persistent virus at undetectable levels. The low turnover of virus, T cells, and B cells constitute a unifying feature of persistent infection, illustrating the dichotomy between distinct immune effectors in regulating acute and persistent central nervous system infection.