Oral immunization of BALB/c mice with Helicobacter pylori lysate combined with dmLT adjuvant for the induction of mucosal and system immune responses
Objective 
To observe the protective effects of oral immunization with Helicobacter pylori (Hp) lysates in combination with mucosal adjuvant dmLT (double mutant heat-labile toxin) against Hp infection in a BALB/c mouse model and to analyze the features of induced immune responses. 
 
 
Methods 
BALB/c mice were orally immunized with Hp lysate (Sydney strain 1, SS1 strain) and dmLT adjuvant, and then innoculated with live Hp strains through oral gavage. A control group was set up by oral administration of normal saline (200 μl/mouse). The colonization of Hp strains in the stomachs of mice was measured six weeks after bacterial inoculation. Samples of serum, spleen, mesenteric lymph node (MLN), small intestine, cecum and feces were collected from mice to analyze the features of induced immune responses. 
 
 
Results 
The colonization of Hp strains in the stomachs of the immunized mice was significantly decreased as compared with that of the control group. Increased specific IgG antibody responses which were predominantly of IgG1 subtype were detected in the serum samples of the immunized mice and the IgG1/IgG2a ratio was significantly higher than that of the control group. Elevated secretory IgA (sIgA) was detected in the samples of small intestine, cecum and feces in the immunization group, especially in the small intestine samples, while no significant change in sIgA secretion was observed in the control group. The percentages of IL-17+ CD4+ T cells in spleen and mesenteric lymph nodes of the immunization group were significantly higher than those of the control group. 
 
 
Conclusions 
Oral immunization with Hp lysates in combination with adjuvant dmLT induced mucosal and systemic immune responses and enhanced the resistance to Hp colonization in BALB/c mice, which was associated with the significantly increased Th17 immune responses and Th2 polarization. This study provided reference for further evaluation of dmLT as a mucosal adjuvant in the development of recombinant protein vaccines against Hp infection. 
 
 
Key words: 
Sydney strain 1 lysate; Double mutant heat-labile toxin (dmLT); BALB/c mouse; Immune response; Helicobacter pylori vaccine