A Focus on Humoral Immunity to Viral Infections

A ntibodies play a central role in the immune system's response to viral infection. They act through a variety of mechanisms, including the blockade of viral entry into host cells and/or the triggering of other components of the immune response. Importantly, because of their ease of elicitation and efficacy against many viruses, they are the primary goal of almost all vaccine strategies. In addition, antibody responses are also important in modern diagnostics. Four papers in the current issue of Viral Immunology highlight practical aspects of antibody responses to viral infections, including the vaccination and diagnostic aspects.

A prime example of a vaccine that elicits protective neutralizing antibodies is the influenza vaccine. This vaccine is particularly important for the control of seasonal influenza in the elderly population, which is at higher risk of death from influenza than the general population. Kositanont and colleagues. have investigated antibody responses elicited by influenza vaccination in a population of elderly individuals in Thailand. The authors show that the vaccinees developed strong influenza virus-specific antibody responses with sustainable titers throughout the 12-month study period. In addition, the presence of pre-existing antibody (presumably from prior infection or vaccination) enhanced the antibody response elicited by the vaccination. These data suggest influenza vaccination can boost anamnestic responses to influenza. In another vaccination study, Meng and colleagues have compared the efficacy of different equine infectious anemia virus (EIAV) vaccines in generating EIAV envelope-specific antibodies. The authors show that DNA/recombinant vaccinia-vectored vaccine did not induce broadly neutralizing antibodies indicating that that other, or additional, envelope sequences may be necessary to induce broadly neutralizing antibodies. Serum antibodies are important diagnostic signatures of prior infection or vaccination. Sun and colleagues have taken advantage of this to assess asymptomatic Dengue virus infection during a Dengue fever outbreak in China. Given that the disease is not endemic in China, the data reveal surprisingly high levels of asymptomatic dengue fever virus infection during the outbreak. Along the same lines, Oje and colleagues. have used serum antibodies to show high rates of dual positivity for hepatitis B virus (HBV) surface antigen and anti-Hepatitis C virus (HCV) antibody in hospital patients of Ekiti State, Nigeria. The authors speculate that unprotected sexual intercourse is the most probable mode of acquisition of HBV and HCV by the seropositive study participants.

While the latter two papers illustrate the diagnostic applications of serum antibodies, other serum proteins are also important diagnostic tools. This is aptly illustrated by a paper from Arendt and colleagues who have monitored serum HBV surface antigen in HBV/human immunodeficiency virus co-infected patients. The authors show that HBsAg declines steadily in the majority of HBV/HIV-patients that are on antiretroviral therapy. They speculate that long-term follow-up of HBV/HIV-co-infected patients will be needed to identify distinct HBsAg patterns.

Finally, a study by Hoebe and colleagues investigates the role of secreted Epstein Barr Virus (EBV)-encoded BARF1 protein in immune evasion. BARF1 protein is a decoy receptor for macrophage colony stimulating factor and interferes with macrophage differentiation and activation. The authors show that soluble BARF1 hampers the function and differentiation of macrophages and contributes to modulation of immune responses in the microenvironment of EBV positive carcinomas.

Taken together, the papers in this strong issue of Viral Immunology highlight the importance of antibodies to vaccines and diagnostics in a variety of infections, hosts, and locations.