An Organotypic Human Lymph Node Model Reveals the Importance of Fibroblastic Reticular Cells for Dendritic Cell Function

BACKGROUND

Human lymph node (HuLN) models have emerged with invaluable potential for immunological research and therapeutic application given their fundamental role in human health and disease. While fibroblastic reticular cells (FRCs) are instrumental to HuLN functioning, their inclusion and recognition of importance for organotypic in vitro lymphoid models remain limited.

METHODS

Here, we established an in vitro three-dimensional (3D) model in a collagen-fibrin hydrogel with primary FRCs and a dendritic cell (DC) cell line (MUTZ-3 DC). To study and characterise the cellular interactions seen in this 3D FRC-DC organotypic model compared to the native HuLN; flow cytometry, immunohistochemistry, immunofluorescence and cytokine/chemokine analysis were performed.

RESULTS

FRCs were pivotal for survival, proliferation and localisation of MUTZ-3 DCs. Additionally, we found that CD1a expression was absent on MUTZ-3 DCs that developed in the presence of FRCs during cytokine-induced MUTZ-3 DC differentiation, which was also seen with primary monocyte-derived DCs (moDCs). This phenotype resembled HuLN-resident DCs, which we detected in primary HuLNs, and these CD1a- MUTZ-3 DCs induced T cell proliferation within a mixed leukocyte reaction (MLR), indicating a functional DC status. FRCs expressed podoplanin (PDPN), CD90 (Thy-1), CD146 (MCAM) and Gremlin-1, thereby resembling the DC supporting stromal cell subset identified in HuLNs.

CONCLUSION

This 3D FRC-DC organotypic model highlights the influence and importance of FRCs for DC functioning in a more realistic HuLN microenvironment. As such, this work provides a starting point for the development of an in vitro HuLN.

Reconstructed Human Skin with Hypodermis Shows Essential Role of Adipose Tissue in Skin Metabolism

BACKGROUND

Dysregulation of skin metabolism is associated with a plethora of diseases such as psoriasis and dermatitis. Until now, reconstructed human skin (RhS) models lack the metabolic potential of native human skin, thereby limiting their relevance to study human healthy and diseased skin. We aimed to determine whether incorporation of an adipocyte-containing hypodermis into RhS improves its metabolic potential and to identify major metabolic pathways up-regulated in adipose-RhS.

METHODS

Primary human keratinocytes, fibroblasts and differentiated adipose-derived stromal cells were co-cultured in a collagen/fibrin scaffold to create an adipose-RhS. The model was extensively characterized structurally in two- and three-dimensions, by cytokine secretion and RNA-sequencing for metabolic enzyme expression.

RESULTS

Adipose-RhS showed increased secretion of adipokines. Both RhS and adipose-RhS expressed 29 of 35 metabolic genes expressed in ex vivo native human skin. Addition of the adipose layer resulted in up-regulation of 286 genes in the dermal-adipose fraction of which 7 were involved in phase I (CYP19A1, CYP4F22, CYP3A5, ALDH3B2, EPHX3) and phase II (SULT2B1, GPX3) metabolism. Vitamin A, D and carotenoid metabolic pathways were enriched. Additionally, pro-inflammatory (IL-1β, IL-18, IL-23, IL-33, IFN-α2, TNF-α) and anti-inflammatory cytokine (IL-10, IL-12p70) secretion was reduced in adipose-RhS.

CONCLUSIONS

Adipose-RhS mimics healthy native human skin more closely than traditional RhS since it has a less inflamed phenotype and a higher metabolic activity, indicating the contribution of adipocytes to tissue homeostasis. Therefore it is better suited to study onset of skin diseases and the effect of xenobiotics.

CD169 Defines Activated CD14+ Monocytes With Enhanced CD8+ T Cell Activation Capacity

Monocytes are antigen-presenting cells (APCs) that play diverse roles in promoting or regulating inflammatory responses, but their role in T cell stimulation is not well defined. In inflammatory conditions, monocytes frequently show increased expression of CD169/Siglec-1, a type-I interferon (IFN-I)-regulated protein. However, little is known about the phenotype and function of these CD169⁺ monocytes. Here, we have investigated the phenotype of human CD169⁺ monocytes in different diseases, their capacity to activate CD8⁺ T cells, and the potential for a targeted-vaccination approach. Using spectral flow cytometry, we detected CD169 expression by CD14⁺ CD16^- classical and CD14⁺ CD16⁺ intermediate monocytes and unbiased analysis showed that they were distinct from dendritic cells, including the recently described CD14-expressing DC3. CD169⁺ monocytes expressed higher levels of co-stimulatory and HLA molecules, suggesting an increased activation state. IFNα treatment highly upregulated CD169 expression on CD14⁺ monocytes and boosted their capacity to cross-present antigen to CD8⁺ T cells. Furthermore, we observed CD169⁺ monocytes in virally-infected patients, including in the blood and bronchoalveolar lavage fluid of COVID-19 patients, as well as in the blood of patients with different types of cancers. Finally, we evaluated two CD169-targeting nanovaccine platforms, antibody-based and liposome-based, and we showed that CD169⁺ monocytes efficiently presented tumor-associated peptides gp100 and WT1 to antigen-specific CD8⁺ T cells. In conclusion, our data indicate that CD169⁺ monocytes are activated monocytes with enhanced CD8⁺ T cell stimulatory capacity and that they emerge as an interesting target in nanovaccine strategies, because of their presence in health and different diseases.

D-xylose catabolism in Bacteroides xylanolyticus X5-1

The xylose metabolism of Bacteroides xylanolyticus X5-1 was studied by determining specific enzyme activities in cell free extracts, by following 13C-label distribution patterns in growing cultures and by mass balance calculations. Enzyme activities of the pentose phosphate pathway and the Embden-Meyerhof-Parnas pathway were sufficiently high to account for in vivo xylose fermentation to pyruvate via a combination of these two pathways. Pyruvate was mainly oxidized to acetyl-CoA, CO2 and a reduced cofactor (ferredoxin). Part of the pyruvate was converted to acetyl-CoA and formate by means of a pyruvate-formate lyase. Acetyl-CoA was either converted to acetate by a combined action of phosphotransacetylase and acetate kinase or reduced to ethanol by an acetaldehyde dehydrogenase and an ethanol dehydrogenase. The latter two enzymes displayed both a NADH- and a NADPH-linked activity. Cofactor regeneration proceeded via a reduction of intermediates of the metabolism (i.e. acetyl-CoA and acetaldehyde) and via proton reduction. According to the deduced pathway about 2.5 mol ATP are generated per mol of xylose degraded.