The effect of improvements in cytometer sensitivity on the detection of CD5-positive B cells with dim fluorescence.

When antigen density on the surface of a cell population is low and variable, the percentage of that population determined to express the antigen (i.e., to be positively stained) depends directly on the sensitivity of the flow cytometer for resolving particles which are dimly fluorescent from those which are unstained. In this study, the sensitivity of a commercial flow cytometer has been improved by changes in the photomultiplier tube, the fluorescence filter, and the amount of stray light entering the fluorescence channel. In a model system with human lymphocytes, modifications to these factors increased the percent of the B-lymphocyte population found to express the CD5 antigen.