The plaque cytogram assay. II. Correlation between morphology and density of linear bovine serum albumin buoyant density gradient-separated immunocompetent cells.

The plaque cytogram assay has been combined with pH 6.8, linear bovine serum albumin (BSA) gradients to demonstrate the correlation between the morphology and buoyant density of immunocompetent cells. Ten types of plaque-forming cells (PFC) and four types of plaques have been identified and enriched in the density gradients. Reproducible density profiles of mouse erythrocytes, lymphoid cells, and PFC have been obtained with BSA gradients. The density peak for mouse erythrocytes was about 1.080 g/ml, while the lymphoid cell density profile had several peaks with a maximum concentration at 1.064 g/ml. Three distinct peaks or shoulders were found in the density profile of hemolytic PFC. Most of the density distributions of the individual morphologic classes of PFC were considerably narrower than that of the entire PFC distribution and were discrete from each other. The combined result that the PFC could be subdivided by morphology and density, and that the two phenomena were correlated establishes that the PFC are truly a heterogeneous population. Whether this heterogeneity is due to different stages in development or due to the existence of differing classes of cells will have to await future experimentation.