Microcytotoxicity assay for cell-mediated immunity enumerating residual target number by 86Rb

Abstract Lymphocyte-mediated lysis of target cells grown as monolayers in microtiter wells is readily quantitated by an assay measuring the 86 Rb incorporated after attaining isotopic equilibrium. Lysis of fibroblasts by allogeneic lymphocytes sensitized by skin grafts and of tumor cells by syngeneic spleen cells sensitized by intraperitoneal tumor inoculation were readily detected. Weakly cytolytic lymphocytpopulations can be assayed by increasing incubation times to 48 h or longer. A potential problem, 86 Rb incorporation by lymphocytes sticking to residual target cells, was controlled by comparing 86 Rb incorporation by targets incubated with non-immune lymphocytes. Results by 86 Rb incorporation were identical to those determined by microscopic counting or 51 Cr release. 86 Rb incorporation assays should be considered as an alternate to 51 Cr release techniques, especially in those experimental systems where the cytolytic potential of a lymphocyte population is so low that lysis can be detected only after long incubation times and/or when the spontaneous release of 51 Cr is prohibitively high.