Heli Uronen‐Hansson

A functionally distinct subset of CD103(+) dendritic cells (DCs) has recently been identified in murine mesenteric lymph nodes (MLN) that induces enhanced FoxP3(+) T cell differentiation, retinoic acid receptor signaling, and gut-homing receptor (CCR9 and alpha4beta7) expression in responding T cells. We show that this function is specific to small intestinal lamina propria (SI-LP) and MLN CD103(+) DCs. CD103(+) SI-LP DCs appeared to derive from circulating DC precursors that continually seed the SI-LP. BrdU pulse-chase experiments suggested that most CD103(+) DCs do not derive from a CD103(-) SI-LP DC intermediate. The majority of CD103(+) MLN DCs appear to represent a tissue-derived migratory population that plays a central role in presenting orally derived soluble antigen to CD8(+) and CD4(+) T cells. In contrast, most CD103(-) MLN DCs appear to derive from blood precursors, and these cells could proliferate within the MLN and present systemic soluble antigen. Critically, CD103(+) DCs with similar phenotype and functional properties were present in human MLN, and their selective ability to induce CCR9 was maintained by CD103(+) MLN DCs isolated from SB Crohn's patients. Thus, small intestinal CD103(+) DCs represent a potential novel target for regulating human intestinal inflammatory responses.

Mouse CD8α(+) dendritic cells (DCs) in lymphoid organs and CD103(+) CD11b(-) DCs in nonlymphoid tissues share phenotypic and functional similarities, as well as a unique shared developmental dependence on the transcription factor Batf3. Human DCs resembling mouse CD8α(+) DCs in phenotype and function have been identified in human blood, spleen, and tonsil. However, it is not clear whether such cells are also present in human nonlymphoid organs, and their equivalence to mouse CD8α(+) DC has recently been questioned. Furthermore, the identification of "CD8α(+) DC-like" cells across different tissues and species remains problematic because of the lack of a unique marker that can be used to unambiguously define lineage members. Here we show that mouse CD8α(+) DCs and CD103(+) CD11b(-) DCs can be defined by shared high expression of DNGR-1 (CLEC9A). We further show that DNGR-1 uniquely marks a CD11b(-) human DC population present in both lymphoid and nonlymphoid tissues of humans and humanized mice. Finally, we demonstrate that knockdown of Batf3 selectively prevents the development of DNGR-1(+) human DCs in vitro. Thus, high expression of DNGR-1 specifically and universally identifies a unique DC subset in mouse and humans. Evolutionarily conserved Batf3 dependence justifies classification of DNGR-1(hi) DCs as a distinct DC lineage.

Intestinal M play an important role in maintaining gut homeostasis. However, little is known about these cells, their precursors, and their role in intestinal inflammation. Here, we characterize the CD14(+) mononuclear cell populations in intestinal mucosa and blood in patients with CD. Among the LP CD14(+) M, we identified three distinct HLA-DR(+)-expressing subsets. Compared with uninflamed, inflamed mucosa contained a marked increase in the proportion of the CD14(hi)HLA-DR(dim) cellular subset. This subset resembled the classical blood monocytes with low CD16, HLA-DR, and CX3CR1 expression. Classical monocytes migrated efficiently toward CCL2 and released the highest levels of MMP-1 and proinflammatory cytokines when stimulated with immune complexes or LPS. Our findings strongly suggest that it is the classical and not the intermediate or nonclassical monocytes that are the precursors to the dominating intestinal CD14(hi)HLA-DR(dim) subset. This enhances our understanding of CD pathology and may provide new options in treatment.