Altered OXPHOS potential in ascites immune cells is linked to CD4 T-cell exhaustion and a higher risk of spontaneous bacterial peritonitis in cirrhosis

Background and aims Ascites marks advanced cirrhosis and increases the risk of complications including SBP. Systemic inflammation in liver disease is well characterized, but the immunometabolic properties of the peritoneal compartment remain undefined. This study evaluated the metabolic characteristics of ascites-derived immune cells. Method Matched blood and ascites samples from patients with cirrhosis without SBP (n = 21) were analyzed. OXPHOS and glycolysis were assessed using the Seahorse XFe96, lactate concentrations were measured, and immune cell subsets were characterized by spectral flow cytometry. Results T cells were the dominant subset in ascites and blood (58.2% vs. 49%, p=0.0822) and CD4 + T cells represented the predominant subset (57.3% vs. 64.6%, p=0.026). Ascites-derived MNCs exhibited higher basal and maximal respiration than blood-counterparts (4.4 vs 3.6, p = 0.033 and 20 vs 13.3 pmol O 2 /min/µg protein, p=0.004). Proton leak was increased in ascites (0.7 vs 0.4 pmol O 2 /min/µg protein, p<0.0001). OXPHOS potential was increased in ascites (365.9% vs. 290.9%, p<0.001) while glycolytic potential was reduced (208.0% vs. 286.8%, p < 0.001), corroborated by lower ascitic lactate concentrations (1.9 vs. 3.8 mM/L, p<0.001). Patients with low ascites OXPHOS potential had higher risk of developing SBP (p = 0.016). CD4 + T cells in ascites showed elevated PD-1 expression (36.9% vs. 14.7%, p < 0.0001), associated with reduced OXPHOS potential (407.1% vs. 324.6% in PD-1-low vs. PD-1-high cells, p = 0.036). Conclusion Peritoneal immune cells exhibit a dissociated phenotype—elevated oxidative activity alongside features of immune exhaustion—reflecting their distinct role in immune regulation within the peritoneal environment.