Long-lasting humoral immune responses by intranasal immunization of OVA plus PMB.

<p>Mice were intranasally immunized with OVA plus 500 µg of PMB 3 times at weekly intervals. One group was intranasally boosted with OVA plus 500 µg of PMB at 13 weeks after the last immunization (closed circle), whereas the other group was intranasally administered with normal saline (open circle). <i>A.</i> The levels of OVA-specific IgA Abs in fecal extracts, as well as IgG and IgA Abs in plasma, were determined by ELISA. Data represent mean ± SD values from 8 mice in each experimental group. <i>B.</i> After 31 weeks, mononuclear cells isolated from the n-LP, i-LP, SMGs, and spleen were determined using an OVA-specific ELISPOT assay. Data represent mean ± SD values of the number of AFCs/10⁶ cells from 8 mice per experimental group. Significant differences between non-boosted (open column) and boosted (closed column) groups are indicated with asterisks (* <i>p</i><0.05 and ** <i>p</i><0.005). ND, not detected.