To test the two hypotheses, we investigated: 1) Whether IL-6 contributes to the impairment of endothelial function in db/db mice; 2) Whether IL-6 and TNF-α interact to cause T2D-induced endothelial dysfunction; 3) The localization of IL-6 in vascular cells; and 4) The cellular mechanisms by which IL-6 mediates endothelial dysfunction in coronary microcirculation in db/db mice. Here, TNF is linked to endothelial dysfunction.