An ex vivo co-culture model of murine skin and lymph nodes to represent psoriatic inflammation and identify novel treatments

Summary: Psoriasis is driven by the IL23-IL17 pathway and involves an amalgamation of cells, such as Th17 cells, keratinocytes, and dendritic cells. <i>In vivo</i> mouse models, such as direct IL23 injection and minicircle DNA are effective tools for translational research; however, the development of <i>ex vivo/in vitro</i> models would enable more focal studies of immune mechanisms involved in Th17 cell activation in the IL23-IL17 pathway. Whole ears are removed from C57BL/6 mice, gently split into dorsal and ventral layers, and immersed in culture medium in a 24-well plate with the inner side facedown, comprising the resident skin cells of the co-culture. Cervical lymph nodes are collected from the same mouse for single-cell suspension and aliquoted to make up the immune cells of the co-culture. Either IL23, TNF, or both are then added. After 4-24 hours incubation, IL17A is measured by ELISA. RT-PCR and flow cytometry are performed for the skin and lymph node samples, respectively, to determine inflammatory markers. Psoriasis initiation is linked to dendritic cells stimulating T cells, which migrate to the epidermis and drive lesion growth. Our co-culture model, simulating this <i>in vivo</i> network, showed high IL17a expression upon IL23 stimulation (50ng/ml) and over 450-fold increase in IL17a mRNA in the skin. In individual cultures, ear skin showed a 60-fold increase in IL17a, while lymph node cultures only showed a 2.5-fold increase. Other Th17-related genes, IL17f and IL22, displayed similar responses, with IL22 absent in lymph node cultures. IL17a mRNA changes began as early as 4 hours post-IL23 stimulation. TNF-α alone did not significantly affect IL17 production, but a synergistic increase was seen with IL23 and TNF-α combined. NBA, a TRPM4 inhibitor, reduced IL17 levels in the presence of IL23 and TNF-α (p<0.001). The <i>ex vivo</i> co-culture model of murine skin and lymph node tissue under cytokine stimulation offers a controlled, reproducible platform for studying psoriasis immunopathology and testing therapeutic interventions. David Wei^{1, 2}, Xuesong Wu¹, Sam Hwang¹ 1. Dermatology, University of California Davis, Sacramento, CA, United States. 2. Touro University California, Vallejo, CA, United States. Translational Studies: Cell and Molecular Biology