ADA2 and systemic lupus erythematosus: The protein is secreted to the extracellular space, and elevated levels of ADA2 have been found—for example, in plasma or pleural effusions in the context of inflammation, infection, or cancer.5, 6, 7, 8 Examples of diseases that are characterized by increased ADA2 levels include tuberculosis, systemic lupus erythematosus, and macrophage activation syndrome.9, 10, 11 Moreover, it has been shown that in children, plasma ADA2 enzyme activity is negatively correlated with age.12