Leukocyte adherence inhibition as measured by a radioisotopic technique for detection of cell‐mediated tumor immunity

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Abstract
It has been previously reported that cell‐mediated tumor immunity may be detected by leukocyte adherence inhibition (LAI) as determined by a visual counting technique in the presence of soluble tumor antigen. In the present experiments leukocyte adherence was measured by a radioisotopic technique. Peripheral blood mononuclear cells from Wistar/Fu rats and lymph‐node cells (LNC) from C3H/J mice were labelled with Technetium 99m (99mTc) and incubated with medium alone and with medium containing tumor antigens (high dilutions of dialyzed tumor homogenates) in the wells of plastic tissue‐culture plates. After incubation, fluid and non‐adherent cells were removed. The ratio of residual radioactivity in wells with antigen to that in wells without antigen was determined. Adherence of blood mononuclear cells from rats bearing syngeneic transplants of a polyoma‐virus‐induced tumor was inhibited by dialyzed homogenates of this tumor. Adherence of blood mononuclear cells from normal rats was not inhibited. Adherence of LNC from mice bearing syngeneic transplants of a 3‐methylcholanthrene (3‐MCA)‐induced fibrosarcoma was inhibited by dialyzed homogenates of this tumor. Adherence of LNC from normal mice or from mice bearing a different 3‐MCA‐induced tumor was not inhibited. These results support the use of LAI as a simple test for cell‐mediated tumor immunity. Measuring relative leukocyte adherence with the radioisotope 99mTc eliminates possible bias in counting and permits multiple replicate determinations with a small number of leukocytes.