Methodological studies of monocyte yeast cell phagocytosis.

Human mononuclear cells were separated in a Ficoll-Isopaque gradient and incubated in glass chambers in a medium of serum in Parker 199. At the end of the incubation time heat-killed, not pre-opsonized yeast cells (YC) were added for phagocytosis. PA was expressed as the median number of YC per monocyte in 100 monocytes. The results of testing various modifications of this method indicate that an appropriate procedure, allowing a sufficient span for measuring 'subnormal' phagocytosis, is incubation of the monocytes in 15 per cent serum for 120 minutes followed by a further incubation with 10(7) YC (in 7.5% serum) for 30 minutes. The sources of variation in the determination of PA of a standard population was studied by analysis of variance. Based on the results of this study, suitable ways to define and express 'normal' and 'low' phagocytic activity were proposed.