Neutrophils are critical immune cells in severe coronavirus disease 2019 (COVID-19). S100 calcium-binding protein A12 (S100A12) is highly expressed in neutrophils during acute inflammation. The aim of this study was to evaluate serum S100A12 levels as a diagnostic and prognostic tool in COVID-19. Serum samples of patients with moderate and severe COVID-19 were collected during 2020 to 2024. Enzyme-linked immunosorbent assay was used to measure serum S100A12 levels in 63 patients with moderate COVID-19, 60 patients with severe disease and 33 healthy controls. Serum S100A12 levels were elevated in moderate COVID-19 compared to controls and were even higher in severe cases. In moderate disease, serum S100A12 levels positively correlated with immune cell counts. While C-reactive protein and procalcitonin are established inflammation markers, they did not correlate with serum S100A12 levels in either patient cohort. Patients with severe COVID-19 and vancomycin-resistant enterococcus (VRE) infection had increased S100A12 levels. Elevated S100A12 levels were also observed in patients with herpes simplex reactivation. Fungal superinfections did not alter S100A12 levels. These data show that serum S100A12 increases in moderate and severe COVID-19 and is further elevated by VRE bloodstream infection and herpes simplex reactivation. Therefore, S100A12 may serve as a novel biomarker for severe COVID-19 and an early diagnostic indicator for bacterial and viral infections.

Background/Objectives: Liver diseases and chronic inflammatory bowel diseases (IBD) are closely associated, particularly primary sclerosing cholangitis (PSC) and ulcerative colitis (UC). In severe cases of PSC, liver transplantation (LT) may be required, just as severe IBD may necessitate biologic therapy. Evidence on combining biologics with post-transplant immunosuppression is limited, particularly regarding hepatotoxicity, infections, and drug–drug interactions. We therefore assessed the safety of biologic therapy for IBD in LT recipients. Methods: In this retrospective, single-center analysis, all patients treated at the inflammatory bowel disease and post–liver transplantation outpatient clinics of the University Hospital Regensburg were screened. Patients with both LT and IBD were included in the analysis. Medical records, laboratory parameters, and imaging studies were reviewed. Conclusions: A total of 17 liver transplant recipients with IBD were identified. Eleven patients had PSC as the underlying liver disease, while the remaining patients had autoimmune hepatitis (AIH), PSC–AIH overlap syndrome, or cryptogenic liver cirrhosis. Three patients had Crohn’s disease, and 14 had ulcerative colitis. Five patients required biologic therapy because of active IBD. Two patients received two sequential biologic agents, whereas one patient received four different biologics during follow-up. No significant safety signals were observed regarding hepatotoxicity, susceptibility to infections, or interactions with concomitant immunosuppressive therapy, including tacrolimus, mycophenolate mofetil, ciclosporin, and prednisolone. No evidence of clinically relevant safety concerns associated with biologic therapy was identified in liver transplant recipients with IBD. Therefore, biologic therapy combined with conventional post-transplant immunosuppression appears feasible and well tolerated in LT recipients with active IBD; larger prospective studies are needed. However, larger prospective studies are needed to confirm these findings.