Innate immune cells, such as intestinal epithelial cells, dendritic cells (DCs), macrophages, granulocytes, and innate lymphoid cells provide a first line of defence to enteric pathogens. To study the role of CX3CR1+ DCs and macrophages in host defence, we infected CX3CR1-GFP animals with Citrobacter rodentium. When transgenic CX3CR1-GFP animals are infected with the natural mouse pathogen C. rodentium, CX3CR1−/− animals showed a delayed clearance of C. rodentium as compared with (age- and sex-matched) wild-type B6 animals. The delayed clearance of C. rodentium is associated with reduced interleukin (IL)-22 expression. In C. rodentium-infected CX3CR1-GFP animals, IL-22 producing lymphoid-tissue inducer cells (LTi cells) were selectively reduced in the absence of CX3CR1. The reduced IL-22 expression correlates with decreased expression of the antimicrobial peptides RegIIIβ and RegIIIγ. The depletion of CX3CR1+ cells by diphtheria toxin injection in CX3CR1-GFP × CD11c.DOG animals confirmed the role of CX3CR1+ phagocytes in establishing IL-22 production, supporting the clearance of a C. rodentium infection.

The ontogenic relationship between the common dendritic cell (DC) progenitor (CDP), the committed conventional DC precursor (pre-cDC), and cDC subpopulations in lymphoid and nonlymphoid tissues has been largely unraveled. In contrast, the sequential steps of plasmacytoid DC (pDC) development are less defined, and it is unknown at which developmental stage and location final commitment to the pDC lineage occurs. Here we show that CCR9 ؊ pDCs from murine BM which enter the circulation and peripheral tissues have a common DC precursor function in vivo in the steady state, in contrast to CCR9 ؉ pDCs which are terminally differentiated. On adoptive transfer, the fate of CCR9 ؊ pDC-like precursors is governed by the tissues they enter. In the BM and liver, most transferred CCR9 ؊ pDClike precursors differentiate into CCR9 ؉ pDCs, whereas in peripheral lymphoid organs, lung, and intestine, they additionally give rise to cDCs. CCR9 ؊ pDC-like precursors which are distinct from precDCs can be generated from the CDP. IntroductionDendritic cells (DCs) are essential initiators of immunity and link innate to adaptive antimicrobial immune responses. DCs are also critically involved in maintaining immune tolerance against selfAgs and harmless environmental Ags to prevent autoimmune and inflammatory reactions. 1 Murine DCs found in lymphoid and nonlymphoid tissues in the steady state can be broadly classified into tissue-resident conventional or classic DCs (cDCs) and plasmacytoid DCs (pDCs). DCs residing in nonlymphoid tissues are also called migratory DCs because of their ability to migrate and carry Ags derived from the tissues to lymph nodes via lymphatics. CDC subpopulations residing in the spleen and lymph nodes comprise 2 major functionally distinct subpopulations, the CD8␣ ϩ CD11b Ϫ cDCs (which are efficient in cross-presenting Ags to CD8 ϩ T cells), and the CD8␣ Ϫ CD11b ϩ cDCs which are potent stimulators of Th-cell responses. 1 Likewise, 2 major distinct subpopulations can be found in nonlymphoid tissues, namely CD103 ϩ and CD11b ϩ cDCs. 2,3 CD103 ϩ CD11b Ϫ cDCs in nonlymphoid tissues, such as skin, lung, and intestine are functional equivalents of CD8␣ ϩ CD11b Ϫ splenic cDCs, 4-7 while the relationship of nonlymphoid tissue CD11b ϩ DCs to CD8␣ Ϫ CD11b ϩ cDCs remains unclear.PDCs are found in BM and blood as well as in peripheral lymphoid and nonlymphoid organs. Interestingly, the frequency of pDCs among all CD11c ϩ DCs is high in the BM and in the liver, but much lower in spleen, lymph nodes, and other organs. PDCs are functionally characterized by producing high amounts of type I IFNs in response to viruses, which they sense via TLRs 7 and 9. 8 There is evidence that in addition to their role in secreting IFNs and inflammatory cytokines, pDCs can function as APCs. 9 Depending on their localization, activation state, and mechanism of Ag internalization, pDCs can induce protective adaptive immunity or immune tolerance. [10][11][12] PDCs in the liver, for example, play a central role for induction of tolerance to oral...

Dendritic cells (DCs) and macrophages populate the intestinal lamina propria to initiate immune responses required for the maintenance of intestinal homeostasis. To investigate whether CX3CR1(+) phagocytes communicate with CD4 T cells during the development of transfer colitis, we established an antigen-driven colitis model induced by the adoptive transfer of DsRed OT-II cells in CX3CR1(GFP/+) × RAG(-/-) recipients challenged with Escherichia coli expressing ovalbumin (OVA) fused to a cyan fluorescent protein (CFP). After colonization of CX3CR1(GFP/+) × RAG(-/-) animals with red fluorescent E. coli pCherry-OVA, colonic CX3CR1(+) cells but not CD103(+) DCs phagocytosed E. coli pCherry-OVA. Degraded bacterial-derived antigens are transported by CD103(+) DCs to mesenteric lymph nodes (MLNs), where CD103(+) DCs prime naive T cells. In RAG(-/-) recipients reconstituted with OT II cells and gavaged with OVA-expressing E. coli, colonic CX3CR1(+) phagocytes are in close contact with CD4 T cells and presented bacterial-derived antigens to CD4 T cells to activate and expand effector T cells.

In order to meet the challenges in data evaluation and comparability between studies in multiple myeloma (MM) minimal residual disease (MRD) assessment, the goal of the current study was to provide a step-by-step evaluation of next-generation sequencing (NGS) and multicolor flow cytometry (MFC) data. Bone marrow (BM) sample pairs from 125 MM patients were analyzed by NGS and MFC MM MRD methods. Tumor load (TL) and limit of detection (LOD) and quantification (LOQ) were calculated. The best-fit MRD cut-off was chosen as 1 × 10−5, resulting in an overall 9.6% (n overall = 12 (NGS n = 2, MFC n = 10)) nonassessable cases. The overall concordance rate between NGS and MFC was 68.0% (n = 85); discordant results were found in 22.4% (11.2% (n = 14) of cases in each direction. Overall, 55.1% (n = 60/109) and 49.5% (n = 54/109) of patients with a serological response ≥ very good partial response (VGPR) showed BM MRD negativity by NGS and MFC, respectively. A good correlation in the TL assessed by both techniques was found (correlation coefficient = 0.8, n = 40, p < 0.001). Overall, our study shows good concordance between MM BM MRD status and TL when comparing NGS and MFC at a threshold of 10–5. However, a sufficient number of analyzed events and calculation of MRD key metrics are essential for the comparison of methods and evaluability of data at a specific MRD cut-off.