A distinct subset of intestinal dendritic cells responds selectively to oral TLR7/8 stimulation

Abstract

The intestinal innate immune system continually interacts with commensal bacteria, thus oral vaccines should induce extra/alternative activation of DC, potentially through TLR. To examine this we collected intestinal lymph DC (iL-DC) under steady-state conditions and after feeding resiquimod (R-848), a synthetic TLR7/8 ligand, which we showed induces complete emptying of gut DC into lymph. iL-DC are heterogeneous with subset-specific functions. In this study we determined the kinetics of iL-DC subset release, activation and cytokine secretion induced by R-848. We show that L-DC comprise three distinct subsets (CD172a high , CD172a int and CD172a low ) present with similar frequencies in intestinal but not hepatic lymph. No iL-DC express TLR7 mRNA, and only CD172a + iL-DC express TLR8. However, after oral R-848 administration, output of all three subsets increases dramatically. CD172a high DC release precedes that of CD172a low DC, and the increased frequency of CD25 high iL-DC is restricted to the two CD172a + subsets. After feeding R-848 only CD172a high iL-DC secrete IL-6 and IL-12p40. However, CD172a int and CD172a high DC secrete similar but markedly lower amounts when stimulated in vitro. These results highlight the importance of in vivo approaches to assess adjuvant effects on DC and give novel insights into the subset-specific effects of an oral TLR ligand on intestinal DC.

Systemic Flagellin Immunization Stimulates Mucosal CD103+ Dendritic Cells and Drives Foxp3+ Regulatory T Cell and IgA Responses in the Mesenteric Lymph Node

“…The mechanism of R848 action is known to be through an indirect activity on plasmacytoid DCs. These cells then secrete high levels of type I IFN, which in turn acts on CD103 + DCs resulting in their activation and migration to the MLN (30,36). We hypothesize that the ability of sFliC to drive CD103 DC migration to the MLN is through the direct ligation of TLR5 on LP CD103 + DCs.…”

“…The selective migration of CD103 + DCs to the MLN after sFliC immunization occurred despite Ag being systemically administered. Although atypical for systemic adjuvants, this has been demonstrated after immunization with some subunit oral adjuvants such as R848 and Escherichia coli heat-labile enterotoxin (30,39). Additionally, the B subunit of heat-labile enterotoxin can induce cells with a regulatory phenotype after intranasal administration (40), although it is not clear if these are primed by CD103 + DCs.…”

Gastrointestinal Dendritic Cells Promote Th2 Skewing via OX40L

“…Induction of DC migration by CT has been demonstrated by Shreedhar et al (23), who observed that fluorescent microsphereloaded DCs in the subepithelial dome relocated to T cell areas after feeding CT. MacPherson and colleagues have directly addressed the migration of DCs from the intestinal lamina propria by collecting lymph over time in cannulated rats (24 -26). They have shown that DC migration from the lamina propria to the MLN occurs constitutively and that this migration can be modulated by TLR agonists, in particular TLR4 and TLR7/8 agonists (24,25). However, they recently reported that another bacterial toxin with adjuvant activity (heat-labile enterotoxin from Escherichia coli) did not influence DC migration (26).…”

Immunity to gastrointestinal nematode infections

“…121 Similarly, the MAP3 (mitogen-activated protein kinase kinase kinase) kinase TPL-2 was also shown to modulate immunity to H. polygyrus, as its deletion in dendritic cells resulted in enhanced resistance to infection that was attributed to its downstream influence on the homing of leukocytes. 122 Indeed, different dendritic cell subsets have divergent expression of certain cytokine and pattern-recognition receptors, [123][124][125][126] and might thus be inherently more or less prone to respond to specific pathogens and cytokines to begin with. These types of signals, in combination with cell-extrinsic cues from epithelial and innate immune cells, could determine which type of dendritic cell that gets activated upon parasite infection.…”