Hyaluronidase-sensitive halos around adherent cells. Their role in blocking lymphocyte-mediated cytolysis

A variety of adherent sarcoma, carcinoma and normal cells are surrounded in vitro by thick, transparent zones (approximately equal to 9 micron thick) that spleen cells and a variety of other cells and particles cannot penetrate. Seven lymphoblastoid cell lines did not possess such halos. The presence of these halos around adherent fibrosarcoma cells appeared to protect them from lymphocyte-mediated cytolysis. Hyaluronidase treatment, which destroyed the halo and allowed lymphocytes to approach the tumor cell membrane, enhanced the cytotoxic action of immune but not of normal spleen cells. These observations, in addition to highlighting a little-known feature of the cell surface, may also be of general relevance to the in vitro and in vivo killing of tumor cells by immune effector cells.