FCGR1A and Sepsis: CD64 is an IgG-binding receptor expressed by neutrophils, monocytes, and macrophages in response to cytokines released during bacterial infection; given that its expression is upregulated in the early stages of activation of the innate immune response, it performs particularly well as a diagnostic marker of sepsis [122], although its use might be limited by flow cytometry, the method used for CD64 detection, requiring specialized laboratory equipment.