The immune response to rabies virus infection and vaccination

Abstract

Infection with rabies virus causes encephalitis in humans that has a case fatality rate of almost 100%. This inability to resolve infection is surprising since both pre-exposure vaccination and, if given promptly, post-exposure vaccination is highly effective at preventing encephalitic disease. The principal immunological correlate of protection produced by vaccination is neutralizing antibody. T-helper cells contribute to the development of immunity whereas cytotoxic T cells do not appear to play a role in protection and may actually be detrimental to the host. One reason for a failure to protect in humans may be the poor immunological response the virus provokes, despite the period between exposure to virus and the development of disease being measured in months. Few individuals have measurable neutralizing antibody on presentation with disease, although in many cases this develops as symptoms become more severe. Furthermore, when antibody is detected in serum it rarely appears in cerebrospinal fluid suggesting limited penetration into the CNS, the site where it is most needed. The role of the modest mononuclear cell infiltrate into the brain parenchyma is unclear. Some studies suggest the virus can suppress cell-mediated immunity early during the infection although there is little mechanistic evidence to support this beyond suppression of intracellular interferon production by the viral phosphoprotein. In contrast, levels of antibody in the CNS correlate to the peak virus production within the CNS. Here we review the current understanding of immune responses to rabies infection and vaccination against this disease. This article identifies a need to understand how rabies antigens are initially presented and how this can influence the subsequent development of antibody responses. This could help identify ways in which the response to prophylactic vaccination can be enhanced and how the natural immune response to infection can be boosted to combat neuroinvasion.