The surface properties of a tumor line which undergoes a cyclic change in reactivity with cytotoxic T lymphocytes (CTLs) have been analyzed. The findings indicate that MOPC-315-EL when transplanted into the peritoneum of a BALB/c mouse for 4-5 days (early MOPC315-EL) becomes sensitive to lysis by anti-H-2d CTL. After 9 to 10 days of growth in the peritoneal cavity these tumor cells (late MOPC-315-EL) become unreactive to CTLs. The amount of H-2 antigens on the surface of the cells is the same on the early and late tumor cells. By scanning electron microscopy (SEM) we have shown that the early population is a mixture of two cell types which are characterized by surface villi or surface blebs; the late cells are essentially one population which are characterized by surface villi. The net charge on the surface of the cell was evaluated by two methods: (i) rate of cell migration across an electric potential and (ii) binding by cationic ferritin to the glycocalyx. Both techniques indicated that the early cells have a higher net negative charge. The implication of this work is that surface charge may be involved in T cell-target cell interactions.
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