Strain specific maturation of Dendritic cells and production of IL-1ß controls CD40-driven colitis.

Intestinal integrity is maintained by balanced numbers of CD103+ Dendritic cells (DCs), which generate peripherally induced regulatory T cells (iTregs). We have developed a mouse model where DC-specific constitutive CD40 signals caused a strong reduction of CD103+ DCs in the lamina propria (LP) and intestinal lymph nodes (LN). As a consequence, also iTregs were strongly reduced and transgenic mice on the C57Bl/6-background (B6) developed fatal colitis. Here we describe that transgenic mice on a pure Balb/c-background (B/c) do not show any pathologies, while transgenic C57Bl/6 x Balb/c (F1) mice develop weak colon inflammation, without fatal colitis. This graded pathology correlated with the effects of CD40-signalling on DCs in each background, with striking loss of CD103+ DCs in B6, but reduced in F1 and diminished in B/c background. We further show direct correlation of CD103+ DC-numbers with numbers of iTregs, the frequencies of which behave correspondingly. Striking effects on B6-DCs reflected robust loss of surface MHCII, known to be crucial for iTreg induction. Furthermore, elevated levels of IL-23 together with IL-1, found only in B6 mice, support generation of intestinal IFN-γ+IL-17+ Th17 cells and IFN-γ+ Th1 cells, responsible for onset of disease. Together, this demonstrates a novel aspect of colitis-control, depending on genetic background. Moreover, strain-specific environmental sensing might alter the CD103+ DC/iTreg-axis to tip intestinal homeostatic balance to pathology.

Constitutive CD40 Signaling in Dendritic Cells Limits Atherosclerosis by Provoking Inflammatory Bowel Disease and Ensuing Cholesterol Malabsorption.

The costimulatory molecule CD40 is a major driver of atherosclerosis. It is expressed on a wide variety of cell types, including mature dendritic cells (DCs), and is required for optimal T-cell activation and expansion. It remains undetermined whether and how CD40 on DCs impacts the pathogenesis of atherosclerosis. Here, the effects of constitutively active CD40 in DCs on atherosclerosis were examined using low-density lipoprotein-deficient (Ldlr-/-) bone marrow chimeras that express a transgene containing an engineered latent membrane protein 1 (LMP)/CD40 fusion protein conferring constitutive CD40 signaling under control of the DC-specific CD11c promoter (DC-LMP1/CD40). As expected, DC-LMP1/CD40/Ldlr-/- chimeras (DC-LMP1/CD40) showed increased antigen-presenting capacity of DCs and increased T-cell numbers. However, the mice developed extensive neutrophilia compared to CD40wt/Ldlr-/- (CD40wt) chimeras. Despite overt T-cell expansion and neutrophilia, a reduction in conventional DC frequency and a dramatic (approximately 80%) reduction in atherosclerosis was observed. Further analyses revealed that cholesterol and triglyceride levels had decreased by 37% and 60%, respectively, in DC-LMP1/CD40 chimeras. Moreover, DC-LMP1/CD40 chimeras developed inflammatory bowel disease characterized by massive transmural influx of leukocytes and lymphocytes, resulting in villous degeneration and lipid malabsorption. Constitutive activation of CD40 in DCs results in inflammation of the gastrointestinal tract, thereby impairing lipid uptake, which consequently results in attenuated atherosclerosis.

CD40-signalling abrogates induction of RORγt+ Treg cells by intestinal CD103+ DCs and causes fatal colitis.

Immune homeostasis in intestinal tissues depends on the generation of regulatory T (Treg) cells. CD103+ dendritic cells (DCs) acquire microbiota-derived material from the gut lumen for transport to draining lymph nodes and generation of receptor-related orphan γt+ (RORγt+) Helios--induced Treg (iTreg) cells. Here we show CD40-signalling as a microbe-independent signal that can induce migration of CD103+ DCs from the lamina propria (LP) to the mesenteric lymph nodes. Transgenic mice with constitutive CD11c-specific CD40-signalling have reduced numbers of CD103+ DCs in LP and a low frequency of RORγt+Helios- iTreg cells, exacerbated inflammatory Th1/Th17 responses, high titres of microbiota-specific immunoglobulins, dysbiosis and fatal colitis, but no pathology is detected in other tissues. Our data demonstrate a CD40-dependent mechanism capable of abrogating iTreg cell induction by DCs, and suggest that the CD40L/CD40-signalling axis might be able to intervene in the generation of new iTreg cells in order to counter-regulate immune suppression to enhance immunity.

Novel spontaneous deletion of artemis exons 10 and 11 in mice leads to T- and B-cell deficiency.

Here we describe a novel, spontaneous, 4035 basepairs long deletion in the DNA cross-link repair 1C (Dclre1c)-locus in C57BL/6-mice, which leads to loss of exons 10 and 11 of the gene encoding for Artemis, a protein involved into V(D) J-recombination of antigen receptors of T and B cells. While several spontaneous mutations of Artemis have been described to cause SCID in humans, in mice, only targeted deletions by knockout technology are known to cause the same phenotype so far. The deletion we observed causes a loss of Artemis function in the C57BL/6 strain and, consequently, the absence of T and B cells, in presence of normal numbers of NK cells and cells of the myeloid lineage. Thus, for the first time we present T(-)B(-)NK(+) severe combined immunodeficiency (SCID) phenotype after spontaneously occurring modification of Artemis gene in mice. Our mouse model may serve as a valuable tool to study mechanisms as well as potential therapies of SCID in humans.