Jean-Daniel Fauny

Respiratory infectious diseases are among the leading causes of global morbidity and mortality and remain a major public health concern. Progress in understanding early host-pathogen interactions has been hampered by the limited physiological relevance of existing experimental systems. Different models mimicking the human respiratory epithelium have been developed to study viral infections in vitro , such as tridimensional (3D) tissue models and organoids. However, many lack key features of human tissue architecture, particularly the lamina propria or immune cells. To address these limitations, we established an immunocompetent 3D model of the human respiratory mucosa by combining nasal epithelial cells isolated from nasal brushings, fibroblasts from mid-turbinate nasal biopsies, and macrophages derived from blood monocytes. These cells were sequentially seeded into collagen-chitosan scaffolds, resulting in a reconstructed respiratory mucosa closely resembling the in vivo nasal tissues. To further confirm the physiological relevance of the model, we infected it with influenza A virus. The mucosa model supported viral replication in the epithelium and consequently showed increased secretion of inflammatory cytokines and upregulation of type I interferon related genes, enabling the monitoring of early antiviral innate immune responses in a physiologically relevant context.

Macroautophagy (often-named autophagy), a catabolic process involving autophagy-related (Atg) genes, prevents the accumulation of harmful cytoplasmic components and mobilizes energy reserves in long-lived and self-renewing cells. Autophagy deficiency affects antigen presentation in conventional dendritic cells (DCs) without impacting their survival. However, previous studies did not address epidermal Langerhans cells (LCs). Here, we demonstrate that deletion of either Atg5 or Atg7 in LCs leads to their gradual depletion. ATG5-deficient LCs showed metabolic dysregulation and accumulated neutral lipids. Despite increased mitochondrial respiratory capacity, they were unable to process lipids, eventually leading them to ferroptosis. Finally, metabolically impaired LCs upregulated proinflammatory transcripts and showed decreased expression of neuronal interaction receptors. Altogether, autophagy represents a critical regulator of lipid storage and metabolism in LCs, allowing their maintenance in the epidermis.

Macroautophagy (often-named autophagy), a catabolic process involving autophagy-related ( Atg ) genes, prevents accumulation of harmful cytoplasmic components and mobilizes energy reserves in long-lived and self-renewing cells. Autophagy deficiency affects antigen presentation in conventional dendritic cells (DCs) without impacting their survival. However, previous studies did not address epidermal Langerhans cells (LCs). Here, we demonstrate that deletion of either Atg5 or Atg7 in LCs leads to their gradual depletion. ATG5-deficient LCs showed metabolic dysregulation and accumulated neutral lipids. Despite increased mitochondrial respiratory capacity, they were unable to process lipids, eventually leading them to ferroptosis. Finally, metabolically impaired LCs upregulated proinflammatory transcripts and showed decreased expression of neuronal interaction receptors. Altogether, autophagy represents a critical regulator of lipid storage and metabolism in LCs, allowing their maintenance in the epidermis.

Background: Immune modulation by vitamin D3 through dendritic cells (DCs) remains controversial. Human DCs exposed in vitro counteract type‐1 T‐helper (Th1) differentiation and induce regulatory T cells. However, cutaneous application on mice promotes Th2‐driven inflammation resembling atopic dermatitis and relying on thymic stromal lymphopoietin (TSLP) from keratinocytes and T‐cell orientation by TSLP‐stimulated skin DCs. We studied the effects of vitamin D3 in human skin, focusing on TSLP production and the role of skin DCs in T‐cell differentiation.Methods: Human healthy skin explants were exposed in vitro to vitamin D3 analogs. Migrating DCs were analyzed and TSLP quantified in the supernatant. Allogeneic naïve CD4+ T cells were cocultured with DCs to assess their proliferation and cytokine production.Results: Vitamin D3 induced skin DCs to differentiate Th2 cells producing IL‐4 and IL‐13. Vitamin D3 triggered TSLP release in ~30% of skin explants, correlating with IL‐13 detection in Th2 cells. In these donors, blocking TSLP receptor during skin explant cultures abrogated IL‐13 production, yet IL‐4+ Th2 cells were unaffected. Among skin DCs emerged CD14+ cells that had responded directly to vitamin D3 and differed from classical CD14+ dermal emigrants. Vitamin D3‐elicited CD14+ DCs sufficed to promote IL‐4+ Th2 cells in a TSLP‐independent manner.Conclusion: Vitamin D3, despite inducing TSLP in some donors, had a direct influence on skin DCs, affecting their phenotype and ability to drive Th2 responses independently of TSLP. Our findings pave the way toward in vitro systems that accurately model human cutaneous Th2 responses, notably involved in atopic dermatitis.