Distribution of the thrombomodulin antigen in the rabbit vasculature

The purpose of this study was to determine the distribution of the thrombomodulin (TM) antigen in the rabbit vasculature in vivo. Acetone-fixed, frozen sections of various tissues (brain, heart, aorta, lung, liver, spleen, kidney, small intestine, large intestine, skeletal muscle, bone, and skin) were stained by indirect immunofluorescence with goat affinity-purified antibodies to TM. Both large and small vessels (including capillaries) had demonstrable TM antigen localized to the endothelium while vascular smooth muscle and connective tissue cells were negative. The parenchyma of the organs examined were also negative. Based on antibody dilutions and brightness of staining, there is an indication that lung, followed by heart and intestinal vessels, has the highest concentration of antigen; kidney glomerular capillary loops have the least. These results also indicate that TM is an excellent cell type-specific marker of endothelial cells as the endothelium of all vessels and vascular beds was positive.