- Activation of T lymphocytes and macrophages is an early event in the parthenogenesis of SSc. Activated T cells , macrophages and endothelial cells are important sources of Macrophage Migration Inhibitory Factor MIF was initially identified as the protein secreted by activated T lymphocytes capable of inhibiting random migration of macrophages, concentrating macrophages at inflammation loci, and enhancing their ability to kill intracellular parasites and tumoral cells.