RBP4 and tuberculosis: Nonetheless, there was also evidence that the process, at least in its initial stages, was not exclusively to TB, as close examination of the microarray data at early time points reveals there was expression of primitive (yolk sac) and definitive endodermal gene markers, such as AFP (alpha-fetoprotein), RBP4 (retinol binding protein 4) and FGG (fibrinogen-γ).