By Levi Clancy for Student Reader on
The cell-mediated lympholysis assay (aka CML) assays CTL ability to lyse target cells. The target population (meant for lysis) is incubated in Na251CrO4, thus labeling the cells intracellularly with chromium-51 (aka 51Cr). The 51Cr cannot diffuse back out of the cells, so the only way 51Cr can be released back into the supernatent is if the target cells are lysed.
When activated CTLs are incubated for 1-4 hours with washed target cells (to remove unabsorbed Na251CrO4) the amount of 51Cr in the supernatent correlates directly to the extent of target cell lysis by the CTLs. Thus, the specificity of CTLs for allogeneic cells tumor cells, virus-infected cells and artificially modified cells can be assayed. CTLs will typically only lyse cells of the same MHC Class I haplotype.