CCL3 and bacterial pneumonia: The interactions between chemokines and their receptors (e.g., CCL3_CCR5 axis) is crucial for directing T cells to the sites of infection.35 During infection, persistent signaling through CCR5 can lead to continuous T cell activation, potentially resulting in T cell exhaustion and reduced functionality.36 Thus, understanding these interactions between M-MDSCs (Macro_03_M1) and T cell subtypes provides insights into potential therapeutic strategies to enhance immune function in severe bacterial pneumonia.