*Purpose: Although many cytokines are upregulated within allografts undergoing rejection, intragraft transcripts are dominated by IFN-response signatures. Resolution is a key phase of inflammation needed to reduce accumulation of immune cells at local sites, followed by restoration of normal function. Failure to attenuate this process leads to a detrimental, chronic response and maladaptive immunity that underlies many inflammatory diseases, including chronic allograft rejection. Blood endothelial cells (EC) actively regulate access of leukocytes to peripheral tissues and regulate egress in response to inflammatory insult. Much has been studied on the initiation of inflammation during endothelial activation, but less is known about the kinetics and mechanisms necessary for the return to a non-inflamed state.

*Methods: We examined the profile, kinetics and contraction of type II endothelial activation by NFκB-driven TNFα and JAK/STAT-mediated IFNγ. Endothelial pro-adhesive phenotypes were compared under chronic cytokine stimulation (1-48hr), and upon short-term cytokine priming (3hr) followed by withdrawal (up to 48hr). We tested HMEC-1 and primary human endothelial cells from 6 different vascular beds. Endothelial activation was measured at the mRNA and protein levels by Nanostring, flow cytometry, ELISA and multiplex Luminex assays. JAK1/2 was inhibited with ruxolitinib (20nM-2μM).

*Results: TNFα promoted early expression of E-selectin, VCAM-1, ICAM-1, and broad biphasic induction of chemokines. IFNγ upregulated ICAM-1, BST2 and a restricted set of CXCL chemokines. The dynamics of endothelial adhesive phenotype changes after withdrawal were also distinct. A small proportion of TNFα-induced endothelial phenotype changes persisted, but most other effects required continuous TNFα exposure for reinforcement. In contrast, the consequences of even short exposure (3hr) to IFNγ were long-lasting and broad, with sustained elevation of adhesion molecules and chemokines 48hr later. NFκB genes and target transcriptional changes were quickly down-regulated in the absence of TNFα, while JAK, STAT and IRF gene expression was durable, dependent on new transcription but independent of continuous IFNγ exposure. Finally, intact persistent JAK signaling in the endothelium was required to maintain a pro-adhesive phenotype after IFNγ withdrawal, which could be prevented by the JAK1/2 inhibitor ruxolitinib.

*Conclusions: Our results reveal a sustained perturbation of endothelial function and pro-adhesive phenotype after exposure to IFNγ, mediated by JAK and dependent on new transcription. The resolution of endothelial-controlled inflammation may therefore be impaired or delayed under JAK conditions, but quiescence more readily re-established when perturbation was dependent on NFκB. JAK antagonism may therefore represent a novel therapeutic approach to dampening intragraft inflammation.

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