Mesangial cells and their matrix form the central stalk of the glomerulus and are part of a functional unit interacting closely with endothelial cells and podocytes. Alterations in one cell type can produce changes in the others. The cytokines generated by mesangial cells, endothelial cells, and podocytes that tridirectionally and interactively influence cognate receptors on receiver cells are not fully defined. The existence of cytokine cross-talk seems very likely, given the observations that podocyte injury frequently results in mesangial cell proliferation, whereas mesangial cell injury leads to foot process fusion and proteinuria. Another potentially fruitful area of future research is the role of mesangial cells as local modulators of innate and adaptive immune responses. Thus, mesangial cell research still holds much promise.