KAPOSIS-SARCOMA CELLS EXPRESS THE MACROPHAGE-ASSOCIATED ANTIGEN MANNOSE RECEPTOR AND DEVELOP IN PERIPHERAL-BLOOD CULTURES OF KAPOSIS-SARCOMA PATIENTS

The mannose receptor (MR) is a surface 175-kd C-type lectin expressed by macrophages and dendritic cells. MR is involved in removal of effet e cells, phagocytosis of mannose-coated particles, pinocytosis, and an tigen presentation. Expression of MR was investigated in 17 biopsies o f Kaposi's sarcoma (3 AIDS KS, 13 classical KS, and 1 transplant-assoc iated KS) using three anti-MR monoclonal antibodies (3.29, D547, and P AM1). Immunostaining for MR was detected in 94 +/- 7% KS cells with sp indle morphology. In normal tissues, MR was expressed by sinus-linking cells of spleen and lymph nodes, but it was not detected in endotheli al cells lining normal hematic and lymphatic vessels, hemangioma, hema ngioendothelioma, and lymphangioma. Expression of MR in KS cells promp ted us to investigate the possibility that they derive from a circulat ing precursor cell. Peripheral blood mononuclear cells from 16 patient s with KS (10 classical, 1 transplanted, and 5 AIDS) were cultured in PHA-conditioned medium for 10 to 14 days. Confluent monolayers of adhe rent spindle cells were detected in 8 of 11 classical KS, in 5 of 5 AI DS KS patients, and in 0 of 34 control patients. Peripheral-blood-deri ved KS-like cells were characterized by co-expression of macrophage an d endothelial antigens being positive for CD45 (60%), CD68 (98%), MR ( 70%), CD14 (25%), VE-cadherin (70%), and von Willebrand factor (10%). When the immunophenotype of peripheral-blood-derived adherent cells wa s compared with that of KS spindle cells of tissue biopsies, it was fo und that both cell types are VE-cadherin(+)/MR(+)CD68(+), that periphe ral-blood-derived spindle cells are CD34(-) and are less frequently st ained for CD31 and von Willebrand factor, and that lesional KS cells d o not express the leukocyte markers CD45 and CD18. Our findings are co nsistent with the possibility that KS lesions derive from tissue accum ulation and local proliferation of a special subset of macrophages wit h endothelial features the normal counterpart of which are the sinus-l ining cells of spleen and lymph nodes.