Macrophage and dendritic cell subsets in IBD: ALDH+ cells are reduced in colon tissue of patients with ulcerative colitis regardless of inflammation.

Disruption of the homeostatic balance of intestinal dendritic cells (DCs) and macrophages (MQs) may contribute to inflammatory bowel disease. We characterized DC and MQ populations, including their ability to produce retinoic acid, in clinical material encompassing Crohn's ileitis, Crohn's colitis and ulcerative colitis (UC) as well as mesenteric lymph nodes (MLNs) draining these sites. Increased CD14(+)DR(int) MQs characterized inflamed intestinal mucosa while total CD141(+) or CD1c(+) DCs numbers were unchanged. However, CD103(+) DCs, including CD141(+)CD103(+) and CD1c(+)CD103(+) DCs, were reduced in inflamed intestine. In MLNs, two CD14(-) DC populations were identified: CD11c(int)HLADR(hi) and CD11c(hi)HLADR(int) cells. A marked increase of CD11c(hi)HLADR(int) DC, particularly DR(int)CD1c(+) DCs, characterized MLNs draining inflamed intestine. The fraction of DC and MQ populations expressing aldehyde dehydrogenase (ALDH) activity, reflecting retinoic acid synthesis, in UC colon, both in active disease and remission, were reduced compared to controls and inflamed Crohn's colon. In contrast, no difference in the frequency of ALDH(+) cells among blood precursors was detected between UC patients and non-inflamed controls. This suggests that ALDH activity in myeloid cells in the colon of UC patients, regardless of whether the disease is active or in remission, is influenced by the intestinal environment.

A major population of mucosal memory CD4+ T cells, coexpressing IL-18Rα and DR3, display innate lymphocyte functionality.

Mucosal tissues contain large numbers of memory CD4(+) T cells that, through T-cell receptor-dependent interactions with antigen-presenting cells, are believed to have a key role in barrier defense and maintenance of tissue integrity. Here we identify a major subset of memory CD4(+) T cells at barrier surfaces that coexpress interleukin-18 receptor alpha (IL-18Rα) and death receptor-3 (DR3), and display innate lymphocyte functionality. The cytokines IL-15 or the DR3 ligand tumor necrosis factor (TNF)-like cytokine 1A (TL1a) induced memory IL-18Rα(+)DR3(+)CD4(+) T cells to produce interferon-γ, TNF-α, IL-6, IL-5, IL-13, granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-22 in the presence of IL-12/IL-18. TL1a synergized with IL-15 to enhance this response, while suppressing IL-15-induced IL-10 production. TL1a- and IL-15-mediated cytokine induction required the presence of IL-18, whereas induction of IL-5, IL-13, GM-CSF, and IL-22 was IL-12 independent. IL-18Rα(+)DR3(+)CD4(+) T cells with similar functionality were present in human skin, nasal polyps, and, in particular, the intestine, where in chronic inflammation they localized with IL-18-producing cells in lymphoid aggregates. Collectively, these results suggest that human memory IL-18Rα(+)DR3(+) CD4(+) T cells may contribute to antigen-independent innate responses at barrier surfaces.

Resident and pro-inflammatory macrophages in the colon represent alternative context-dependent fates of the same Ly6Chi monocyte precursors.

Macrophages (mφ) are essential for intestinal homeostasis and the pathology of inflammatory bowel disease (IBD), but it is unclear whether discrete mφ populations carry out these distinct functions or if resident mφ change during inflammation. We show here that most resident mφ in resting mouse colon express very high levels of CX3CR1, are avidly phagocytic and MHCII(hi), but are resistant to Toll-like receptor (TLR) stimulation, produce interleukin 10 constitutively, and express CD163 and CD206. A smaller population of CX3CR1(int) cells is present in resting colon and it expands during experimental colitis. Ly6C(hi)CCR2(+) monocytes can give rise to all mφ subsets in both healthy and inflamed colon and we show that the CX3CR1(int) pool represents a continuum in which newly arrived, recently divided monocytes develop into resident CX3CR1(hi) mφ. This process is arrested during experimental colitis, resulting in the accumulation of TLR-responsive pro-inflammatory mφ. Phenotypic analysis of human intestinal mφ indicates that analogous processes occur in the normal and Crohn's disease ileum. These studies show for the first time that resident and inflammatory mφ in the intestine represent alternative differentiation outcomes of the same precursor and targeting these events could offer routes for therapeutic intervention in IBD.

Directed antigen targeting in vivo identifies a role for CD103+ dendritic cells in both tolerogenic and immunogenic T-cell responses.

The αE integrin chain CD103 identifies a subset of migratory dendritic cells (DCs) in the gut, lung, and skin. To gain further understanding of the function of CD103(+) DCs in regulating adaptive immunity in vivo, we coupled ovalbumin (OVA) to the CD103 antibody M290 (M290.OVA). Intraperitoneal injection of M290.OVA induced OVA-specific CD8(+) and CD4(+) T-cell proliferation in lymph nodes (LNs) of wild-type but not CD103(-/-) mice, or in mice depleted of CD11c(+) cells. In the absence of maturation stimuli, systemic antigen targeting to CD103(+) DCs led to tolerance of CD8(+) T cells, whereas coadministration of adjuvant induced cytotoxic T-lymphocyte (CTL) immunity and antibody production. Mucosal intratracheal application of M290.OVA also induced T-cell proliferation in mediastinal LNs, yet the functional outcome was tolerance that inhibited subsequent development of allergic airway inflammation and immunoglobulin E (IgE) responses to inhaled OVA. These findings identify antigen targeting to CD103(+) DCs as a potential strategy to regulate immune responses in nonlymphoid mucosal tissues.

Growth hormone enhances proinflammatory cytokine production by monocytes in whole blood.

Growth hormone (GH) has been used as anabolic therapy to treat catabolic patients. In a recent study, however, administration of high doses of GH to critically ill adults was associated with an increase in morbidity and mortality. Preponderance of septic shock and uncontrolled infections as causes of death in these patients suggests an immuno-modulatory effect of GH. Our hypothesis was that GH treatment may modulate the production of proinflammatory cytokines, which are implicated in sepsis. In our study, human monocytes in whole blood were activated with lipopolysaccaharide (LPS) (1-100 ng/ml) purified from a clinical isolate of group B Neisseria meningitidis in the presence of a high dose of GH (100 ng/ml). The subsequent proinflammatory cytokine response was analysed by intracellular cytokine staining and flow cytometry. Our results show that GH enhances IL1-alpha, IL-6 and TNF-alpha production by LPS activated monocytes in whole blood. The modulation of cytokines by GH may be responsible for the adverse consequences of GH in critically ill patients.