A hepatic network of dendritic cells mediates CD4 T cell help outside lymphoid organs

While CD4+ T cells are a prerequisite for CD8+ T cell-mediated protection against intracellular hepatotropic pathogens, the mechanisms facilitating the transfer of CD4-help to intrahepatic CD8+ T cells are unknown. Here, we developed an experimental system to investigate cognate CD4+ and CD8+ T cell responses to a model-antigen expressed de novo in hepatocytes and reveal that after initial priming, effector CD4+ and CD8+ T cells migrate into portal tracts and peri-central vein regions of the liver where they cluster with type-1 conventional dendritic cells. These dendritic cells are locally licensed by CD4+ T cells and expand the number of CD8+ T cells in situ, resulting in larger effector and memory CD8+ T cell pools. These findings reveal that CD4+ T cells promote intrahepatic immunity by amplifying the CD8+ T cell response via peripheral licensing of hepatic type-1 conventional dendritic cells and identify intrahepatic perivascular compartments specialized in facilitating effector T cell-dendritic cell interactions.

The liver contains distinct interconnected networks of CX3CR1 + macrophages, XCR1 + type 1 and CD301a + type 2 conventional dendritic cells embedded within portal tracts

Portal tracts are key intrahepatic structures where leukocytes accumulate during immune responses. They contain the blood inflow, which includes portal blood from the gut, and lymphatic and biliary outflow of the liver, and as such represent a key interface for potential pathogen entry to the liver. Myeloid cells residing in the interstitium of the portal tract might play an important role in the surveillance or prevention of pathogen dissemination; however, the exact composition and localization of this population has not been explored fully. Our in‐depth characterization of portal tract myeloid cells revealed that in addition to T lymphocytes, portal tracts contain a heterogeneous population of MHCII^high myeloid cells with potential antigen presenting cell (APC) function. These include a previously unreported subset of CSF1R‐dependent CX3CR1⁺ macrophages that phenotypically and morphologically resemble liver capsular macrophages, as well as the two main dendritic cell subsets (cDC1 and cDC2). These cells are not randomly distributed, but each subset forms interconnected networks intertwined with specific components of the portal tract. The CX3CR1⁺ cells were preferentially detected along the outer border of the portal tracts, and also in the portal interstitium adjacent to the portal vein, bile duct, lymphatic vessels and hepatic artery. cDC1s abounded along the lymphatic vessels, while cDC2s mostly surrounded the biliary tree. The specific distributions of these discrete subsets predict that they may serve distinct functions in this compartment. Overall, our findings suggest that portal tracts and their embedded cellular networks of myeloid cells form a distinctive lymphoid compartment in the liver that has the potential to orchestrate immune responses in this organ.

Abstract 5167: Rab27a promotes melanoma cell invasion and metastasis via the regulation of exosome secretion

Introduction: The Rab GTPase family has been increasingly related to carcinogenesis and cancer biology during the past decade. In melanoma, Rab27a has been identified as a tumor dependency gene. Rab27a is thought to regulate exosome secretion in several cell types, however the exact role of Rab27a in melanoma biology and the underlying mechanisms are not well investigated.

Experimental Procedures: To investigate the influence of Rab27a on melanoma biology and exosome secretion, Rab27a shRNA knockdown (KD) or CRISPR knockout (KO) was performed in human and murine melanoma cell lines. The effect of Rab27a loss on melanoma cell invasion and motility was analyzed by in vitro 3D spheroid invasion and live cell imaging. Rab27a function on melanoma metastasis was investigated using a mouse melanoma spontaneous metastasis model. Exosomes secreted by melanoma cell lines with/without Rab27a KD/KO were purified and characterized by electron microscopy, NanoSight analysis, BCA assay, western blotting and mass spectrometry.

Results: Our results indicate that Rab27a loss in Rab27a high metastatic melanoma cell lines reduced 3D spheroid invasion and cell motility and Rab27a loss also reduced spontaneous melanoma metastasis in vivo. Rab27a KD invasion phenotype can be partially rescued by addition of exosomes from Rab27a replete cell conditioned media, but not exosomes derived from Rab27a KD cells. Loss of Rab27a does not alter the number of exosomes secreted from melanoma cells, but does alter exosome protein composition and morphology. Mass spectrometry analysis has shown that Rab27a replete cell secreted exosomes are more involved in regulating cell invasion and motility than the exosomes from Rab27a KD cells.

Conclusion: In summary, Rab27a promotes the invasion and metastasis of a subset of melanoma cells via the regulation of pro-invasive exosomes, which indicates Rab27a as a potential therapeutic target for preventing melanoma progression.

Citation Format: DAJIANG GUO, Goldie Y. Lui, Danae M. Sharp, Siew Li Lai, Shweta Tikoo, Rain Kwan, Michelle van Geldermalsen, Jeff Holst, Nikolas K. Haass, Wolfgang Weninger, Kimberley A. Beaumont. Rab27a promotes melanoma cell invasion and metastasis via the regulation of exosome secretion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5167.

Multiphoton intravital microscopy visualization of skin graft rejection in real time (126.14)

The current paradigm explaining organ graft rejection postulates that rejection is initiated by graft resident dendritic cells that reach the draining lymph nodes via lymphatics and activate naive alloreactive T cells. These newly activated T cells then migrate into the graft. However up to half the T cells recognizing allogeneic MHC in adult animals are already be of memory phenotype, and thus capable of direct entry into a graft site without prior activation in LNs. This is not the result of previous exposure to allo-Ag, but stems from the fact that the allo-MHC-specific and Ag-specific T cell receptor repertoires overlap each other. These pre-existing allo-reactive T cells represent a major barrier to organ transplantation. To understand the contributions of memory cells to skin graft rejection, we are using intravital multiphoton microscopy to track cellular interactions between memory cells, DCs and lymphatic and vascular endothelium during graft rejection and acceptance. Preliminary studies suggest that DCs from grafts are unable to exit the surgical site, most likely as a result of surgical disruption of lymphatic drainage from the transplanted skin. Further work will investigate trafficking of graft-reactive CD4 effector and Treg cells into the graft site.

MEKK1 is essential for DT40 cell apoptosis in response to microtubule disruption

Vinblastine and other microtubule-damaging agents, such as nocodazole and paclitaxel, cause cell cycle arrest at the G2/M transition and promote apoptosis in eukaryotic cells. The roles of these drugs in disrupting microtubule dynamics and causing cell cycle arrest are well characterized. However, the mechanisms by which these agents promote apoptosis are poorly understood. We disrupted the MEKK1 kinase domain in chicken bursal B-cell line DT40 by homologous recombination and have shown that it is essential for both vinblastine-mediated apoptosis and vinblastine-mediated c-Jun N-terminal protein kinase activation. In addition, our data indicate that vinblastine-mediated apoptosis in DT40 cells requires new protein synthesis but does not require G2/M arrest, suggesting that vinblastine-mediated cell cycle arrest and apoptosis are two independent processes.

Characterization of the cytoplasmic domain of interleukin-13 receptor-alpha

Interleukin (IL)-13 and IL-4 are pleiotropic immunoregulatory cytokines that share many overlapping biological properties reflecting the fact that both can utilize a receptor complex composed of the IL-4 receptor-alpha (IL-4Ralpha) chain and the IL-13Ralpha chain. The cytoplasmic domain of the IL-13Ralpha is 60 amino acids long and is essential for IL-13-dependent growth. It contains a Pro-rich domain in the membrane-proximal region and two Tyr residues. Here we show that a truncated IL-13Ralpha, lacking the 38 carboxyl-terminal residues but retaining the Pro-rich region, can support IL-13-dependent proliferation, although with reduced efficiency. A Y402F mutant of the cytoplasmic domain of IL-13Ralpha supported normal IL-13-induced growth. However, tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3), which we show is induced by IL-13 and IL-4 in cells that express the IL-13Ralpha, was significantly reduced. The cytoplasmic domain of IL-13Ralpha was constitutively associated with STAT3, Tyk2, and Janus kinase 1 (JAK1). IL-13-induced tyrosine phosphorylation of IL-13Ralpha in vivo could not be detected using anti-Tyr(P) antibodies. A glutathione S-transferase fusion protein of the cytoplasmic domain of IL-13Ralpha was phosphorylated on tyrosine in vitro by JAK1, JAK3, and Tyk2, although the tyrosine phosphorylation events mediated by Tyk2 and JAK3 were not detectable using anti-phosphotyrosine antibodies. These data, together with the demonstration that IL-13Ralpha associates constitutively with Tyk2 and that Tyr-402 is involved in IL-13-induced phosphorylation of STAT3, suggest that the latter is mediated by Tyk2. Tyrosine phosphorylation of STAT3, which was not necessary for IL-13-induced proliferation, may account for some of the effects of IL-4 and IL-13 on the function of their targets.

Beneficial effects of dietary carbohydrate restriction in chronic cor pulmonale

To explore the effects of moderate and severe reductions in carbohydrate intake on abnormal pulmonary physiology in chronic hypercapneic respiratory failure, spirometric, metabolic, arterial blood gas tension, and oximetric studies were carried out in eight patients who took, in random order daily for a week, either 50 g or 200 g of carbohydrate in an isocaloric diet. At the end of a week's daily intake of an isocaloric diet containing 200 g of carbohydrate, all patients experienced a subjective improvement; the mean body weight was 55.5 +/- 15.4 kg (1 SD) compared with 56.0 +/- 16.0 kg during the control dietary period, the arterial carbon dioxide tension decreased from a mean of 56.9 +/- 6.7 to 50.9 +/- 6.2 mm Hg (p less than 0.005), and the arterial oxygen tension increased from a mean of 50.6 +/- 7.3 to 62.0 +/- 14.5 mm Hg (p less than 0.02). After a week's intake of 50 g of carbohydrate in an isocaloric diet, the body weight and arterial oxygen tension did not change significantly, but the arterial carbon dioxide tension decreased still further to 48.0 +/- 7.8 mm Hg (p less than 0.05). Mouth pressure at 100 msec after the start of inspiration, as a measure of respiratory center output, was significantly higher during both the low carbohydrate intakes compared with the control dietary period. The spirometric data, ventilation-perfusion distribution measurements, oxygen consumption, and carbon dioxide production did not change significantly during various dietary periods. It is concluded that, under these short-term, hospital-controlled conditions, a reduction in the carbohydrate intake to 200 g a day improves the general well-being of patients with chronic hypercapneic respiratory failure, increases arterial oxygen tension, and decreases arterial carbon dioxide tension. A further reduction in the carbohydrate intake to 50 g a day provides further beneficial effects, and such a diet may be used in patients with intractable respiratory failure.