ObjectiveTo elucidate the causal relationship between immune cells and diffuse large B-cell lymphoma (DLBCL), we conducted a Mendelian randomization analysis.MethodsMendelian randomization (MR) leverages genetic variants as instruments to infer causal effects from observational data. Here, we performed a two-sample MR analysis to assess the causal impact of 731 immune cell types on DLBCL. We employed various MR techniques, including the weighted median estimator (WME) and inverse variance weighting (IVW), and conducted sensitivity analyses to ensure result robustness. Additionally, reverse MR analysis was performed to explore the potential causal relationship between DLBCL and immune cells.ResultsWe identified seventeen immune features with causal links to DLBCL, categorized across various cellular groups: four in B cells, two in T cell maturation stages, six in Tregs, four in the TBNK group, and one in dendritic cells (DCs). Sensitivity analyses confirmed the absence of heterogeneity, horizontal pleiotropy, and bias in our findings. Reverse causal analysis revealed a causal association between DLBCL and one of the seventeen immune cell types identified.ConclusionsOur MR analysis of seventeen immune cell types uncovers the complex interactions between the immune system and DLBCL, providing crucial insights into the tumor microenvironment and potential avenues for targeted immunotherapy.