Hi Mohamed - here are some ideas.
If you are prepared to try out 3D cell culture, you could use separated co-culture in the following ways:
1) Use a scaffold (like the Alvetex well inserts) where you culture one of the cell types in the scaffold (say the monocyte line), add a layer of ECM (like collagen) on the top of the scaffold and then culture the epithelial cell type on the top surface. This will allow you to keep the cell lines separated and study paracrine effects. it also has the benefit of allowing the cells to grow in 3D
2) You can also try simply growing one of the cells in 2D in the bottom of a 6 well or 12 well plate and grow the other cell type in 3D in a hanging Alvetex well insert
3) You coudl grow one type of cell in 3D in an Alvetex plate and the second cell also in 3D in an Alvetex well insert.
Both 2 and 3 above will allow you to use co-culture but study paracrine effects.
Here is an application note that describes some of this -
Kind regards and let me know if you have any questions.