BACKGROUND & AIMS: Patients with chronic HBV infection and concomitant metabolic dysfunction-associated steatohepatitis (MASH) have been shown to develop more severe liver disease than patients with chronic HBV alone. However, our understanding of the underlying mechanisms is limited. Herein, we study how comorbid MASH impacts immune activity in the livers of patients with chronic HBV infection. METHODS: Bulk RNA sequencing was performed on liver biopsies from patients with only MASH (n = 10), only HBeAg-negative chronic HBV (ENEG
n = 11), combined MASH/ENEG (n = 9) and healthy controls (n = 9). Biopsies with no or minimal fibrosis (≤F2) were selected to avoid confounding effects of fibrosis. We compared whole transcriptome data from patients with MASH/ENEG to those with ENEG alone to determine the impact of comorbid MASH on chronic hepatitis B. RESULTS: There is a high degree of overlap of liver gene expression profiles in patients with only ENEG vs. those with only MASH compared to healthy controls, suggesting a largely shared mechanism of liver dysfunction and immune activity for these distinct conditions. In patients with ENEG, comorbid MASH was associated with significantly reduced interferon pathway activity (normalized enrichment score = 2.03, p.adj = 0.0251), the expression of interferon-stimulated genes (e.g., IFIT2, IFI27, IFITM1, IFI6), and macrophage gene signatures (e.g., MARCO, CD163, CD5L, CD63), when compared to patients with ENEG alone. CONCLUSIONS: Transcriptomic profiling of the liver suggests that MASH negatively impacts interferon-stimulated gene expression and macrophage gene signatures in the livers of patients with ENEG, which may affect antiviral immune pathways, viral replication and inflammatory responses, resulting in an increased risk of advanced fibrosis in patients with chronic hepatitis B. Our study provides valuable insights for guiding future research aimed at developing effective, tailored strategies for managing patients with both conditions. IMPACT AND IMPLICATIONS: In recent decades, obesity and associated health issues have reached epidemic levels, with steatotic liver disease affecting up to 30% of adults in developed countries, and this trend is also observed among patients with chronic hepatitis B. Given the high and rising prevalence of steatotic liver disease and its frequent co-occurrence in patients with chronic hepatitis B, it is essential to understand how conditions such as metabolic dysfunction-associated steatohepatitis (MASH) impact immune responses in the liver. This study provides unique insights into the impact of MASH on HBV antiviral immune activity in the livers of patients with chronic hepatitis B. The rising number of patients with both conditions affects treatment outcomes and highlights the urgent need for novel, tailored therapeutic strategies. Our study holds significant relevance for guiding future research on developing treatment strategies for patients with both MASH and chronic hepatitis B.