The REG CCD, N- and C-terminal subdomains and peptides generated antibody titers in rabbits and mice that bound fully glycosylated Recombinant Mammalian expressed G ectodomain (RMG) and intact RSV virion particles but minimal neutralization titers compared with the intact G ectodomain. CCD to RSV-specific immunity. We evaluated the immunogenicity, neutralization and protective efficacy of all RSV-G antigenic sites identified following primary RSV infection using recombinant expressed G ectodomain (REG), CCD-deleted G ectodomain (REG CCD), N- and C-terminal G subdomains, and antigenic site peptides. The REG CCD, N- and C-terminal subdomains and peptides generated antibody titers in rabbits and mice that bound fully Onjisaponin B glycosylated Recombinant Mammalian expressed G ectodomain (RMG) and intact RSV virion particles but minimal neutralization titers compared with the intact G ectodomain. Vaccinated mice were challenged intranasally with RSV-A2 Line 19F. Viral replication in nasal cavity and lungs was significantly reduced in vaccinated animals compared to unimmunized controls. Control Onjisaponin B of viral loads post-RSV challenge correlated with serum antibody binding to the virus particles. In addition, very low Th2/Th1 cytokine ratios were found in the lungs of REG CCD vaccinated mice after challenge. These data demonstrate the presence of multiple protective sites in RSV G protein outside of the CCD that could contribute to the development of a bacterially produced PLA2G5 unglycosylated G protein as safe and protective vaccine against RSV disease. Author summary A vaccine against RSV that provides protection without potential for disease enhancement is required. The G attachment protein represents an important candidate for inclusion in an effective RSV vaccine. However, the contribution of different antigenic sites to protection against RSV is not completely understood. We evaluated the protective efficacy of recombinant unglycosylated RSV-G protein vaccine produced in (REG) vs. CCD-deletion (REG CCD). We also investigated immunogenicity and protective efficacy of all antigenic sites identified in post-primary infection infant sera using GFPDL that includes N- and C-terminal G subdomains, and linear peptides. The REG CCD, N- and C-terminal subdomains and peptides generated antibody titers in rabbits and mice. Vaccinated mice challenged intranasally with RSV demonstrated significant reduction of viral replication in the nasal cavity and lungs. Our Onjisaponin B study highlights the safety and immunogenicity of recombinant G protein as economical protective vaccine against RSV disease. Introduction Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract disease among infants and children globally   . Hospitalizations for respiratory tract disease among young children, especially in less than one year old, is most often attributed to RSV infection . Furthermore, despite the development of immunity following RSV infection during childhood, individuals remain susceptible to RSV upper respiratory tract reinfection life-long[6, 7] . RSV isolates can be classified into two antigenically distinct groups (A and B) with genetic differences occurring mostly in the attachment glycoprotein G (47% heterogeneity at the amino acid level) and to a lesser degree in the fusion protein F (9%) . In addition, continuous evolution of RSV generates diversity primarily in the G gene . Heterologous RSV strains are the main cause of re-infections, and homologous RSV strains are observed less frequently  . However, while there are instances of evolution, e.g. the RSVs with duplications in the G gene, there are also cases of same genotype reappearing over many years. Even though F specific antibodies have been reported to contribute to majority of virus neutralization measure PRNT assays, the relative contribution of F and G specific antibodies to protection is not completely understood. A Onjisaponin B recent study by Capella found that higher concentrations of pre-F and G Onjisaponin B antibodies (but not post-F antibodies) were associated with lower clinical disease severity in infants and young children ( 2yr) . In a previous study, we generated gene fragment phage display libraries (GFPDL) for the RSV surface proteins F and G to elucidate the complete antibody epitope repertoire in serum samples from infants either prior to ( 9 months) or after primary and early RSV infection (15C18 months) . Primary RSV infection predominantly resulted in an increase of G specific binding antibodies as observed by 100-fold increase in the number of phages that bound to the post-RSV infection sera compared with pre-infection sera. Bound phages displayed epitopes that spanned most of the ectodomain of RSV-G with two large conformationally dependent antigenic regions flanking the CCD motif.