Adhesion of lymphocytes to target cells via certain cell surface molecules is important in cytotoxic T lymphocyte-mediated immune reactions. The binding of lymphocyte function-associated (LFA) antigens 1 and 2, with their respective ligands, intercellular adhesion mole-cule-1 (ICAM-1) and LFA-3, which are expressed on the surface of nonlymphoid cells, has been shown to be critical for lymphocyte adhesion. To determine whether basal cell carcinomas (BCCs) can escape immunodetection as a result of the inability of cytotoxic T lymphocytes to bind tumor cells, the expression of adhesion molecules on numerous BCCs, before and after exposure to interferon-γ (IFN-γ), was examined. Ninety-three percent of 30 freshly excised invasive BCCs did not express ICAM-1 and 73% of 11 BCCs did not express LFA-3. However, the normal-appearing basal keratinocytes in epidermis overlying nests of BCC, did express ICAM-1, particularly when a marked LFA-1+and LFA-2+ dermal lymphocytic infiltrate was present. After BCC tissue was incubated in vitro with IFN-γ the expression of ICAM-1 was induced on 85% of tumors studied. Thus tumor cells did not possess an absolute inability to express adhesion molecules; rather the constitutive absence of such molecules may be due to insufficient in vivo cytokine levels necessary to induce expression or a barrier preventing cytokines from reaching and interacting with tumor cells. We conclude that the absence of ICAM-1 and LFA-3 adhesion molecules is a mechanism by which BCCs can avoid immunosurveillance.
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