Role of polymorphonuclear leukocytes in the pulmonary clearance of arrested cancer cells.

Treatment of mice with trypan blue led to an accelerated clearance of 125I-5-iodo-2'-deoxyuridine-radiolabeled B16 melanoma cells arrested in the lungs of tumor-bearing mice and the numbers of pulmonary nodules developing after intravenous injection of nonradiolabeled melanoma cells was reduced. Although macrophage function was normal or depressed in trypan-blue-treated mice, there were increased numbers of circulating polymorphonuclear leukocytes which had increased cytotoxicity for B16 melanoma cells and which produced increased levels of toxic oxygen radical. These findings suggested that polymorphs were responsible for accelerated pulmonary clearance of arrested melanoma cells and this conclusion was supported by the decreased clearance of cancer cells from the lungs of mice treated with antipolymorphonuclear leukocyte antiserum. These studies expand the repertoire of effector cells responsible for determining the extent to which hematogenously disseminated cancer cells are retained in the pulmonary vasculature prior to their extravasation and secondary growth.