Fig. 3.

Protection from lethal challenge after intranasal immunization with the inactivated THpep27 mutant. (A) Mice were intranasally (i.n.) immunized with inactivated THpep27 mutant (1 × 10⁷ colony-forming unit [CFU]) at two-week intervals a total of three times. Sera were collected by bleeding the mice 10 days after the final immunization, and antibody titer to THpep27 lysate was measured by enzyme-linked immunosorbent assay (10 µg/mL lysate protein). (B) Groups of 10 mice were i.n. immunized with either live or inactivated THpep27 mutant (1 × 10⁷) three times, then i.n. challenged 2 weeks after the third immunization with approximately 1 × 10⁷ CFU of the virulent D39 strain. Total mouse Inactivated markerless pep27 mutant as a mucosal vaccine survival was tracked every day and analyzed using GraphPad Prism. NS, not significant. ^**p < 0.01, ^***p < 0.001.