- Expression of smooth muscle cell phenotype by rat mesangial cells in immune complex nephritis. Alpha-smooth muscle actin is a marker of mesangial cell proliferation. Johnson, R.J., Iida, H., Alpers, C.E., Majesky, M.W., Schwartz, S.M., Pritzi, P., Gordon, K., Gown, A.M. J. Clin. Invest. (1991)