IL-6 stimulates production of C4b-binding protein (C4b-BP), a circulating protein that binds to protein S. When C4b-BP levels rise, they sequester more protein S, effectively lowering the free (active) protein S available to act as a cofactor for protein C. This phenomenon is known as an acquired protein S deficiency. The gene discussed is PROS1; the disease is hyperinsulinemic hypoglycemia, familial, 4.