Automated cell count in flow cytometry: a valuable tool to assess CD4 absolute levels in peripheral blood.

The enumeration of lymphocyte subsets in absolute counts has long relied on different methods applied separately to whole blood cell count, lymphocyte differential appreciation, and flow cytometric evaluation of lymphocyte subsets percentages. The development of multicolor labeling methods inflow cytometry now allows a more homogeneous appreciation of several cell subsets among gated lymphocytes. The use of internal calibrators, such as microbead suspensions, also permits a direct appreciation of subsets in absolute counts in a single-platform method. These methods were compared with a traditional multiplatform method of assessing absolute counts of lymphocyte subsets in a pilot study in which all manipulations were performed by 1 person and in a full-scale larger study performed in the normal working conditions of a hospital laboratory. Microspheres seem to be a reliable tool to perform absolute count enumeration inflow cytometry, but several precautions in the sample preparation and flow cytometric analysis are required.

Sequential assessment of cell cycle S phase in flow cytometry: a non-isotopic method to measure lymphocyte activation in vitro.

Lymphocyte multiplication can be induced in vitro by mitogens or specific antigens, and is usually measured using isotopic methods involving tritiated thymidine. Cellular proliferation can also be analyzed by flow cytometry techniques based on cell cycle analysis through the measurement of DNA content. We applied this method to lymphocytes from 113 individuals, to evaluate lymphocyte proliferation after stimulation in vitro by a mitogen (phytohaemagglutinin, PHA) or a recall antigen (tetanus toxoid), using a kinetic approach with four points sequential measurements of the S and G2 phases over six days of culture. The proportion of cells in S phase after PHA stimulation was significantly higher than in controls overall and as early as on day three of the culture. Activation with a recall antigen significantly induced increasing S phase cell proportions up to day six. These data suggest that flow cytometric assessment of the S phase could be a useful alternative to isotopic methods measuring lymphocyte reactivity in vitro.