While assays performed against extracellular M. tuberculosis in standard growth media only partially account for protein binding (7H9 growth medium contains 5% bovine serum albumin fraction V), potency assays against intracellular M. tuberculosis in macrophages contain 10% fetal bovine or human serum, and macrophages largely recapitulate the binding conditions found at the site of infection. Here, ALB is linked to infection.