The development of a radiometric assay for monocyte phagocytosis and killing

Monocyte and macrophage phagocytosis and killing has an important role in host defence against infectious microorganisms. Established methods for investigating these activities in vitro are time-consuming, expensive and prone to subjective error. An in vitro assay has been developed which measures monocyte phagocytosis and killing of Candida albicans. In this system, monocyte function is assessed by a radiometric assay based on the incorporation of [3H]uridine into viable yeast cells. This technique allows the simultaneous but independent measurement of the average number of yeast cells ingested by monocytes and the percentage of the ingested organisms killed within a defined incubation period. These tests can be carried out on a single sample of peripheral blood, are relatively easy to perform, and provide objective results within 24 h of receipt of the specimen. This method gave consistent results when monocyte-enriched harvests were obtained by four different separation techniques. This assay could prove a valuable tool for the investigation of monocyte function in individuals with recurrent infections to determine the contribution this makes to their clinical condition. It may also be used to investigate in vitro the influence of cytokines and other chemical agents on monocyte function.