title: Vaccinia virus extracellular enveloped virion neutralization in vitro and protection in vivo depend on complement.
abstract: Antibody neutralization is an important component of protective immunity against vaccinia virus (VACV). Two distinct virion forms, mature virion and enveloped virion (MV and EV, respectively), possess separate functions and nonoverlapping immunological properties. In this study we examined the mechanics of EV neutralization, focusing on EV protein B5 (also called B5R). We show that neutralization of EV is predominantly complement dependent. From a panel of high-affinity anti-B5 monoclonal antibodies (MAbs), the only potent neutralizer in vitro (90% at 535 ng/ml) was an immunoglobulin G2a (IgG2a), and neutralization was complement mediated. This MAb was the most protective in vivo against lethal intranasal VACV challenge. Further studies demonstrated that in vivo depletion of complement caused a >50% loss of anti-B5 IgG2a protection, directly establishing the importance of complement for protection against the EV form. However, the mechanism of protection is not sterilizing immunity via elimination of the inoculum as the viral inoculum consisted of a purified MV form. The prevention of illness in vivo indicated rapid control of infection. We further demonstrate that antibody-mediated killing of VACV-infected cells expressing surface B5 is a second protective mechanism provided by complement-fixing anti-B5 IgG. Cell killing was very efficient, and this effector function was highly isotype specific. These results indicate that anti-B5 antibody-directed cell lysis via complement is a powerful mechanism for clearance of infected cells, keeping poxvirus-infected cells from being invisible to humoral immune responses. These findings highlight the importance of multiple mechanisms of antibody-mediated protection against VACV and point to key immunobiological differences between MVs and EVs that impact the outcome of infection.
authors.affiliation: Division of Vaccine Discovery, La Jolla Institute for Allergy and Immunology, La Jolla, California 92037, USA.
authors.forename: Mohammed Rafii-El-Idrissi
authors.initials: MR
authors.lastname: Benhnia
authors.forename: Megan M
authors.initials: MM
authors.lastname: McCausland
authors.forename: Juan
authors.initials: J
authors.lastname: Moyron
authors.forename: John
authors.initials: J
authors.lastname: Laudenslager
authors.forename: Steven
authors.initials: S
authors.lastname: Granger
authors.forename: Sandra
authors.initials: S
authors.lastname: Rickert
authors.forename: Lilia
authors.initials: L
authors.lastname: Koriazova
authors.forename: Ralph
authors.initials: R
authors.lastname: Kubo
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Kato
authors.forename: Shane
authors.initials: S
authors.lastname: Crotty
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000235:genetics / Q000276:immunology; D002522:Chlorocebus aethiops; D003165:Complement System Proteins / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D009500:Neutralization Tests; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology; D014616:Vaccinia virus / Q000276:immunology*; D014709:Vero Cells; D014771:Virion / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D011994:Recombinant Proteins; D003165:Complement System Proteins