A microtiter assay for cell-mediated cytotoxicity to cytomegalovirus antigens

The cell-mediated immune response is important to host defense against viruses, yet techniques with which to measure the contribution of lymphocytes (particularly K cells) to anti-viral cytotoxic reactions are not well-established. We describe a new procedure for measuring lymphocyte-mediated antibody-dependent immunity to cytomegalovirus. Central to the assay is the use of 51Cr-containing red blood cells labeled with purified viral antigen, which can be easily quantitated and readily stored for at least 72 hours. High sensitivity was observed, as sera with a 1: 512 complement fixation titer could be diluted 10,000-fold without extinguishing the detectable cytotoxic response. A set of conditions (target/effector ratio; dilution of serum; source and age of target cells; and incubation medium and time) was defined that optimized sensitivity, maintained a low level of background release, yet utilized small amounts of reagents. A kinetics study revealed that 80% of specific release of radioisotope occurred in the first 4 hours. Investigation of the epidemiology, diagnosis, and management of disease caused by CMV may be greatly aided by this new method for quantitating specific cell-mediated anti-viral immune reactivity.