A Heat-labile Enterotoxin B Subunit Mutant (LTB26) of Escherichia coli Enhances Mucosal Immune adjuvanticity via Increased BCR Activity

Heat-labile enterotoxin B subunit (LTB) of is a potential mucosal immune adjuvant for its safety. However, the weaker adjuvant activity fails to meet the clinical requirement. Here, one of LTB mutant numbered LTB26 is constructed with enhanced mucosal immune adjuvanticity than that of LTB wild type (LTB). The transcriptome analysis data suggest that LTB26 enhances mucosal immune adjuvanticity via increased expression of BCR and MHC II molecular. Furthermore, LTB26 can promote both Th1 and Th2 cell mediated immunity via upregulated expression of IL-4 and IFN-γ. Flow cytometry analysis confirms that LTB26 significantly upregulates the activity of antigen presenting cells (DCs and mature macrophage) compared with LTB and LTB57 mutant. The result demonstrates that LTB26 is a potent mucosal immune adjuvant meeting clinical requirement. The GM1 ganglioside (GM1) binding activity of LTB57 is higher than that of LTB26; instead, the immune adjuvanticity of LTB57 is lower than that of LTB26. The result highlights that the immune adjuvanticity of LTB and its mutant are not positively associated with GM1 affinity, which upends decades understanding of the relationship of LTB adjuvanticity and GM1-binding affinity.