Panel A displays the number of studies that examined between one and two, three and five, or more than five peripheral immune biomarkers, underscoring that most existing studies have only investigated a limited number of such biomarkers. Panel B depicts the number of studies and their reported associations for the top 20 most frequently examined peripheral immune biomarkers. Different colors were used for studies based on their reported statistical associations with AD. Evidence supports either a positive or a negative association with AD for eight of these biomarkers, including IL-6, IL-1β, IFN-γ, ACT, IL-18, IL-12, lymphocyte, and IL-6R.