Effect of elicitation on peritoneal macrophage subpopulations: Size distributions, ectoenzyme phenotypes and antitumor activity

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Abstract
Resident (R), Brewer's thioglycollate broth (TG) and C. parvum (CP)‐elicited murine peritoneal cell populations were separated into subpopulations by centrifugation on discontinuous Ficoll gradients consisting of layers of 4, 6, 8 and 10% Ficoll. The resulting subpopulations were shown to be distinct on the basis of cell size, ectoenzyme phenotypes and antitumor activity. The cell size distributions were analyzed by means of a Coulter channelyzer and software developed for a computer. The 4–6% Ficoll interface fraction comprised the smallest macrophages, with most cells in this subpopulation appearing to range in cell volume from 150–275 μm3. The largest sized macrophages were found in the 10%‐pellet fraction, with most cells appearing to range in cell volume from 300–600 μm3. The ectoenzyme phenotypes of the R, TG and CP unseparated macrophage populations were significantly different. Moreover, the ectoenzyme phenotypes of the smallest, (4–6% Ficoll interface) subpopulation in the R and CP macrophages differed from the other subpopulations. Reduction in alkaline phosphodiesterase I (APD‐I) ectoenzyme activity (as compared with unseparated R macrophages) appeared to be a marker for acquisition of antitumor activity. The small CP macrophages (4–6% Ficoll interface) showed no antitumor activity while the unseparated CP macrophages and all other CP macrophages subpopulations exhibited antitumor activity. The CP macrophage unseparated population and the subpopulations with antitumor activity expressed reduced ADP‐I activity. Conversely, the R or TG macrophage unseparated populations and their subpopulations, along with the CP macrophage 4–6% subpopulation, lacked antitumor activity and failed to show a change in ADP‐I ectoenzyme activity.