Blocking of the binding of representative mAb by sera from PR, SC, and DS-Cav1 VLP immunizations. Shown are concentrations (ng/mL) of anti-pre-F IgG in pooled sera obtained at four weeks after boost immunizations with all pre-fusion F VLPs and with RSV infection that blocked 50% binding of mAb AM14 (panel A), D25 (panel B), and palivizumab (panel C) to the soluble DS-Cav1 target protein. Panels D, E, and F show concentrations (ng/mL) of anti-pre-F IgG in pooled sera that blocked binding of mAbs AM14, D25, and palivizumab, respectively, to the soluble SC-TM target protein. The results are the mean of at least three separate determinations, with standard deviations indicated. Comparison of values with those of DS-Cav1 VLP sera was assessed by one-way ANOVA. Panel E DS-Cav1 VLP sera did not block binding of D25, thus values were compared to PR-DM VLP sera; **** p < 0.00005 *** p < 0.0005, ** p < 0.005, * p <0.05. Values at or near 10,000 ng/mL indicate failure of the sera to block binding of the tested mAb. Values at or above 2000 ng/mL indicate sera that only very weakly blocked binding. These values were quite variable from experiment to experiment, as indicated by the large standard deviation, and thus were not included in ANOVA analysis.