Abstract
The LTB of enterotoxigenic Escherichia coli (ETEC) expressed in Bifidobacterium infantis (BI) has been testified as mucosal adjuvant with co-vaccination BI-CfaB (the major fimbrial subunit) together in vivo in our previous study. In order to investigate the mucosal adjuvant effect of BI-LTB to purified antigens, we oral vaccinated SD rats with recombinant BI-LTB plus OVA (rBI-LTB + OVA), and wild type BI plus OVA (wBI + OVA), OVA and PBS (Phosphate buffered saline) were vaccinated as controls, respectively. The OVA-specific sIgA in jejunal mucosa and specific IgG in serium were measured with ELISA (Enzyme-linked immunosorbent assay) and the sIgA producing cells were detected with immunohistochemistry technology (IHC) and Qwin image manipulation tools subsequently. The results shown rBI-LTB could stimulate SD rats produce high titer OVA-specific sIgA in rBI-LTB + OVA group and the OVA-specific sIgA titer in rBI-LTB + OVA group was found significant greater than that of the wBI + OVA group or OVA single group (p < 0.05). However no such significant difference was detected between the group wBI + OVA and OVA. IHC results suggested that intestinal mucosa and submucosa was the main field of sIgA secretion. These results suggested that recombinant LTB expression in BI could be used as a wide range mucosal adjuvant with different form antigens.
Highlights
The LTB of Escherichia coli is one of bacterial products with the greatest potential to function as mucosal adjuvant
The OVA-specific sIgA in jejunal mucosa and specific IgG in serium were measured with ELISA (Enzyme-linked immunosorbent assay) and the sIgA producing cells were detected with immunohistochemistry technology (IHC) and Qwin image manipulation tools subsequently
The results shown recombinant BI-LTB (rBI-LTB) could stimulate SD rats produce high titer OVA-specific sIgA in rBI-LTB + OVA group and the OVA-specific sIgA titer in rBI-LTB + OVA group was found significant greater than that of the wBI + OVA group or OVA single group (p < 0.05)
Summary
The LTB of Escherichia coli is one of bacterial products with the greatest potential to function as mucosal adjuvant. LTB belongs to ADP-ribosylating enterotoxins (cholera toxin and the heat-labile enterotoxin of E. coli) Both LTB and CTB (cholera toxin B subunit) recognize and bind to mucosal cell surface via their receptor GM1-ganglioside existed ubiquitously on the surface of mammalian cells [1,2,3]. The adjuvanticity of LTB has been directly related to GM1-binding activity and the interaction between LTB and the receptor activates B and CD4+ T– cells; and enhances antigen presentation by activating DCs (Dendritic cells) and other APCs (antigen presenting cells) through receptor-mediated endocytosis mechanisms [4] Scientists explain that these molecules exert their adjuvant function by interacting with a variety of cell types, including epithelial cells and DCs, etc. LTB activates selective differentiation of lymphocyte populations and increases presentation on MHC (Major histocompatibility complex) class II, which may be the basis for its adjuvant effect [6,7,8]
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