Target-effector interactions in the rat natural killer cell system. I. The measurement of cytotoxicity at the single cell level.

Abstract

AbstractOptimal conditions have been developed for measuring interactions at the single cell level between effector cells and target cells in the rat NK cell system. Conjugates were formed between splenic leukocytes and target cells to determine the percentage of target binding cells, and after immobilization of the conjugates in agar, single lytic interactions were measured by the uptake of trypan blue by dead target cells. Cytotoxic effector cells were expressed as a percentage of target binding cells. Factors which influenced conjugate formation were the ratio of effector to target cells, temperature, centrifugation and the conditions of culture of the target cells. When comparing a number of rat and mouse strains with various levels of natural killer cell activity, there was found to be a good correlation between the number of target binding cells and cytotoxicity in the standard 51Cr‐release assay in rats, but in mice the removal of nylon‐adherent cells was required to achieve a reasonable correlation. However, 60–70% of the cytotoxicity was lost on nylon fractionation, making this approach of doubtful value. The target‐binding cell and cytotoxic effector cell assays were used in conjunction with the 51Cr‐release assay to study the specificity, rat strain variation and ontogeny of natural killer cells. During ontogeny target binding cells reached adult levels sooner than did cytotoxic effector cells. The greatest development of natural killer cells occurred during the first 3 weeks of life; the number of cytotoxic cells per spleen increased 138‐fold up to 21 days of age, compared with an 11‐fold increase between 21 days and 9 weeks of age.