FIGURE 1.

(A) Direct co-cultures facilitate physical contact between the different cell types which allows for communication though their surface receptors. (B) Indirect co-cultures incorporate a physical separation between cell types only allowing for communication via cell secretomes. (I) Physical separation in the form of a transwell system using a semi-permeable membrane. (II) Conditioned medium is first collected from one cell type and then transferred to the other cell type. The medium contains the cell secretome of the first cell type, which then affects the second cell type.