MNV-3 induces a more robust systemic and mucosal antibody response than MNV-1.

<p><b>A</b>) Clarified supernatants of Sf9 cells infected with recombinant baculoviruses expressing MNV-1 or MNV-3 rVP1/2 were visualized by electron microscopy. The insets show representative VLPs stained with a polyclonal antibody to the MNV-1 VP1 protein using immunogold labeling. <b>B–F</b>) In panels B, C, E and F, groups of mice were inoculated with mock inoculum, 10⁴ TCID₅₀ units of MNV-1, or 10⁴ TCID₅₀ units of MNV-3. In panel D, only mice infected with MNV-3 were tested. In all cases, mice were challenged with homologous inoculum six weeks later. One day later, serum and intestinal contents were collected as described in the <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003592#s4" target="_blank">Methods</a>. <b>B</b>) Serum samples from wild-type B6 mice (a minimum of 4 mice per condition tested in at least two independent experiments) were tested in ELISA on plates coated with the indicated rVP1/2. <b>C</b>) Serum was collected from groups of B6 mice (n = 3) inoculated with either mock inoculum or 10⁴ TCID₅₀ units of the indicated MNV strain for six weeks. The 50% neutralization titer was determined for each serum sample. The entire experiment was repeated three times. Data from all samples per condition were averaged and compared for statistical purposes. <b>D</b>) Serum samples from groups of mice of the indicated knockout strain (a minimum of 4 mice per strain tested in at least two independent experiments) were tested in ELISA on plates coated with either MNV-1 (grey) or MNV-3 (black) rVP1/2. Intestinal contents from the indicated small intestinal piece of wild-type B6 mice (a minimum of 6 mice per condition tested in at least two independent experiments) were tested in ELISA on plates coated with MNV-1 rVP1/2 (<b>E</b>) or MNV-3 rVP1/2 (<b>F</b>). For all panels, the data for all mice in each group were averaged. Statistical analyses were carried out on the indicated groups as described in the <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003592#s4" target="_blank">Methods</a>.