Introduction: Interleukin-18 (IL-18) is a pro-inflammatory cytokine known to contribute to alloimmune responses, but its role in xenotransplantation remains poorly defined. This study investigates IL-18 as both a biomarker of graft injury and a cross-species immune modulator in pig-to-primate kidney xenotransplantation.

Methods: Five genetically engineered pig kidneys were transplanted into rhesus monkeys under conventional immunosuppression. Serum IL-18, creatinine, and platelet counts were measured preoperatively and at endpoint.

Porcine kidney epithelial cells (PK-15) were incubated with recombinant human IL-18. Activation of signaling pathways (MAPK, NF-κB, STAT3, PI3K/AKT/mTOR) was assessed by Western blot, and inflammatory gene expression (e.g., MCP-1, IL-8) and costimulatory molecule (CD40) expression were analyzed by qPCR.

In addition, porcine kidney tissue sections (cortex area) were incubated with human IL-18 for future transcriptomic (bulk RNA-seq) and histological (TUNEL) analyses, which are currently in progress.

Results: At the endpoint, IL-18 levels significantly increased from baseline (0.218 to 218.066 pg/mL; p<0.01), accompanied by a rise in serum creatinine (p<0.01) and a marked reduction in platelet count (from 273.6 to 33.5 ×10³/μL; p<0.01). A positive correlation was observed between IL-18 and creatinine levels (p<0.05, R² = 0.12), whereas no correlation was found with platelet counts.

In vitro, human IL-18 activated porcine kidney cells, leading to phosphorylation of p38 MAPK and NF-κB signaling, but not STAT3 or PI3K/AKT/mTOR indicating selective inflammatory signaling. This resulted in increased expression of MCP-1, IL-8, and CD40, indicating direct immune-stimulatory potential.

Conclusion: This study presents the first combined in vivo and in vitro evidence for the dual role of IL-18 in xenotransplantation. IL-18 levels are significantly elevated following pig-to-monkey kidney xenotransplantation and correlate with graft dysfunction. Human IL-18 can directly activate porcine renal cells via p38 MAPK and NF-κB signaling, driving inflammatory gene expression. These findings support IL-18 as both a biomarker and a therapeutic target in managing xenograft-associated inflammation. Ongoing tissue-level studies will further clarify the downstream consequences of IL-18 signaling in xenografts.