Tie receptor expression on endothelial cells and transfected CHO cells. Cell lysates were prepared as described in Materials and Methods and immunoprecipitated with anti-tie MoAb 5D2. Immunoprecipitates were analyzed by SDS-PAGE and immunoblotted with another anti-tie MoAb, 21G6. Molecular weight markers as indicated. CHO^-, CHO cells transfected with vector alone; CHO, cl.2, CHO cells transfected with full-length tie receptor, clone 2; CHO, cl.37, CHO cells transfected with full-length tie receptor, clone 37; HUVEC, human umbilical vein endothelial cells; MDEC; human microvascular dermal endothelial cells. Double arrows, tie receptor doublet.