Splenic Marginal Zone Dendritic Cells Mediate the Cholera Toxin Adjuvant Effect: Dependence on the ADP-Ribosyltransferase Activity of the Holotoxin

Abstract

The in vivo mechanisms of action of most vaccine adjuvants are poorly understood. In this study, we present data in mice that reveal a series of critical interactions between the cholera toxin (CT) adjuvant and the dendritic cells (DC) of the splenic marginal zone (MZ) that lead to effective priming of an immune response. For the first time, we have followed adjuvant targeting of MZ DC in vivo. We used CT-conjugated OVA and found that the Ag selectively accumulated in MZ DC following i.v. injections. The uptake of Ag into DC was GM1 ganglioside receptor dependent and mediated by the B subunit of CT (CTB). The targeted MZ DC were quite unique in their phenotype: CD11c+, CD8α−, CD11b−, B220−, and expressing intermediate or low levels of MHC class II and DEC205. Whereas CTB only delivered the Ag to MZ DC, the ADP-ribosyltransferase activity of CT was required for the maturation and migration of DC to the T cell zone, where these cells distinctly up-regulated CD86, but not CD80. This interaction appeared to instruct Ag-specific CD4+ T cells to move into the B cell follicle and strongly support germinal center formations. These events may explain why CT-conjugated Ag is substantially more immunogenic than Ag admixed with soluble CT and why CTB-conjugated Ag can tolerize immune responses when given orally or at other mucosal sites.

Intradermal immunization in the ear with cholera toxin and its non‐toxic β subunit promotes efficient Th1 and Th17 differentiation dependent on migrating DCs

“…Here, we report the activation of skin DCs by CT and also with the CTB. This is in contrast with a previous report where spleen DCs were activated by the CT but not by CTB [21]. It has been reported that LCs remain in the epidermis for 48 h, even in the presence of Th1-polarizing adjuvants [7].…”

“…5) since the combination of TGF-b and IL-6 has been reported as crucial in the Th17 differentiation [28]. Interestingly, we also observed IFN-g and IL-17 CD4 1 T-cell differentiation after immunization with the CTB subunit, which argues against previous data that indicated that the adjuvant role of CT is mediated by CT a subunit activity [21]. However, the use of CT as an adjuvant has yielded conflicting data [24,29,30].…”

“…This dominance of IL-17 was also observed in response to the CT b subunit (CTB). Although the precise mechanism for the adjuvant effect of CT is not completely understood, it appears that CTB targets DCs in vivo by binding to the cell membrane ganglioside GM1 [20]; moreover, the CT a subunit (CTA) triggers the PKA-mediated induction of cAMP, which plays a critical role in the subsequent induction of Th17 [21].…”

“…This dominance of IL-17 was also observed in response to the CT b subunit (CTB). Although the precise mechanism for the adjuvant effect of CT is not completely understood, it appears that CTB targets DCs in vivo by binding to the cell membrane ganglioside GM1 [20]; moreover, the CT a subunit (CTA) triggers the PKA-mediated induction of cAMP, which plays a critical role in the subsequent induction of Th17 [21].Following skin immunization, both migrating and LN resident cells can cooperate in T-cell priming [22], and the delayed-type hypersensitivity (DTH) response seems to be dependent on migrating cells [23]; however, the dominant CD4 1 T-cell immune response that is elicited after cutaneous immunization and the role of migrating DCs in the presence of adjuvants needs to be further evaluated. Here, we used intradermal (i.d.)…”

GITR contributes to the systemic adjuvanticity of the Escherichia coli heat‐labile enterotoxin

“…Several studies point to DC as the principal cellular target of LT and CT adjuvanticity in vivo [12,13]. Both toxins induce the maturation of DC, increasing their antigen presentation capability, their migration to the lymph nodes and their interaction with naive T cells [14].…”