MyD88 Signaling Regulates Steady-State Migration of Intestinal CD103+ Dendritic Cells Independently of TNF-α and the Gut Microbiota

Abstract

Intestinal homeostasis and induction of systemic tolerance to fed Ags (i.e., oral tolerance) rely on the steady-state migration of small intestinal lamina propria dendritic cells (DCs) into draining mesenteric lymph nodes (MLN). The majority of these migratory DCs express the α integrin chain CD103, and in this study we demonstrate that the steady-state mobilization of CD103+ DCs into the MLN is in part governed by the IL-1R family/TLR signaling adaptor molecule MyD88. Similar to mice with complete MyD88 deficiency, specific deletion of MyD88 in DCs resulted in a 50–60% reduction in short-term accumulation of both CD103+CD11b+ and CD103+CD11b− DCs in the MLN. DC migration was independent of caspase-1, which is responsible for the inflammasome-dependent proteolytic activation of IL-1 cytokine family members, and was not affected by treatment with broad-spectrum antibiotics. Consistent with the latter finding, the proportion and phenotypic composition of DCs were similar in mesenteric lymph from germ-free and conventionally housed mice. Although TNF-α was required for CD103+ DC migration to the MLN after oral administration of the TLR7 agonist R848, it was not required for the steady-state migration of these cells. Similarly, TLR signaling through the adaptor molecule Toll/IL-1R domain-containing adapter inducing IFN-β and downstream production of type I IFN were not required for steady-state CD103+ DC migration. Taken together, our results demonstrate that MyD88 signaling in DCs, independently of the microbiota and TNF-α, is required for optimal steady-state migration of small intestinal lamina propria CD103+ DCs into the MLN.

β8 Integrin Expression and Activation of TGF-β by Intestinal Dendritic Cells Are Determined by Both Tissue Microenvironment and Cell Lineage

“…To determine whether the intestinal microbiota contributed to induction of αvβ8 expression in DCs, we treated mice with antibiotics, which reduced the presence of microbes in the intestine by 16-fold, assessed by measurement of 16S rDNA in stool (Figure 4A). As expected based on previous studies (22), intestinal CD103 + CD11b − DCs were present and migrated normally to the MLN of antibiotic-treated animals; however, they expressed significantly lower levels of Itgb8 than MLN DCs from untreated mice (Figure 4B–C), indicating a role for the intestinal microbiota in conditioning of these regulatory DCs. We next analyzed Itgb8 expression in intestinal DCs from mice deficient in Myd88 and Trif , components of the Toll-like receptor (TLR) signaling pathway by which DCs sense microbes.…”

“…CD103 + CD11b − DCs in the MLN are composed of cells that develop in the intestinal LP and then migrate (21), and others that reside in the MLN, and these populations can be distinguished by relative levels of CD11c and MHC-II expression (22). Previous findings by ourselves and others that CD103 + DCs derived from the LP can preferentially activate TGF-β in an αvβ8-dependent mechanism (8, 9) suggested that DCs may acquire expression of αvβ8 in the LP.…”

“…To investigate this further, we analyzed expression of Itgb8 in DCs from Ccr7 −/− mice. CCR7 is required for migration of DCs from the LP to MLN (6, 23, 24) and MLN of Ccr7 −/− mice contain predominantly blood-derived DCs with reduced numbers of DCs that have migrated from the intestine ((22) and figure 2B). Notably, the expression of Itgb8 was much lower in CD103 + CD11b − DCs from Ccr7 −/− cells than in cells from control mice, and was not significantly different from expression on CD103 + CD11b + DCs (Figure 2C).…”

Cellular Innate Immunity: An Old Game with New Players

“…The individual composition of the microbiota thus adds another layer of complexity in the regulation and function of the innate immune system [196,[201][202][203][204] in both health and disease [196,205,206] . Seminal findings support an impact of the microbiome on (i) innate immune cells (neutrophils [36,207] , DCs [208][209][210][211][212][213][214][215][216][217] , macrophages [218][219][220] , ILCs [198,[221][222][223][224][225] , NK cells [226] , and NKT cells [227] ), (ii) the complement system [228] , and (iii) defensins [196,229,230] . A major challenge in the field that remains is to define the critical microbiotato-host interfaces that fine-tune the human immune system and to exploit their therapeutic potential.…”

Clients and Oncogenic Roles of Molecular Chaperone gp96/grp94

“…Whereas TLR3, TLR7, TLR8, TLR9 and TLR13 are localized primarily within endolysosomes and recognizes nucleic acids [35], the rest of the TLR family proteins are present on the cell surface and they largely recognize microbial membrane components. TLRs are also expressed on various immune cells, including T and B cells [36, 37], dendritic cells (DCs) [38], macrophages [39] as well as some non-immune cells such as fibroblasts and epithelial cells [40]. Upon encounter with specific microbial molecules TLR receptor are activated and initiate downstream signaling via MyD88-dependent or -independent pathways [41].…”